an interview with don hedeker - center for health … with don hedeker 2016.pdf · an interview...

An interview with Don Hedeker

Juned Siddique1

Received: 2 March 2016 / Accepted: 14 July 2016 / Published online: 23 July 2016� Springer Science+Business Media New York 2016

Abstract Don Hedeker was born in the late 1950s in Chicago, Illinois. He attended public

schools in Chicago and did his undergraduate work at the University of Chicago, earning a

degree in Economics in 1980. In 1981, he began graduate work in the Department of

Behavioral Sciences, Committee on Research Methodology and Quantitative Psychology

at the University of Chicago. He completed his dissertation in 1989 under the direction of

Darrell Bock. In 1993, Don accepted a faculty position at the University of Illinois at

Chicago (UIC) where he was promoted to tenured Associate Professor in 1996 and to Full

Professor in 2001. He spent 20 years on the faculty at UIC, leaving in 2014 in order to

return to the University of Chicago as a Professor of Biostatistics in the Department of

Public Health Sciences. Don’s main expertise is in the development and dissemination of

advanced statistical methods for clustered and longitudinal data. In addition to many

methodological papers in these areas, Don has developed several freeware computer

programs for statistical analysis of such data. To date, he has published over 180 papers

and 1 book. Don is also an accomplished musician, and has played in bands since high

school. This interview was conducted in honor of Don being awarded the 2015 Long-term

Excellence Award from the Health Policy Statistics Section of the American Statistical

Association. The interview took place in Don’s office at the University of Chicago on

December 23, 2015.

Keywords University of Chicago � Mixed-effects models � Darrell Bock � Robert

Gibbons � The Polkaholics

& Juned [email protected]

1 Department of Preventive Medicine, Northwestern University, Chicago, IL, USA

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Health Serv Outcomes Res Method (2016) 16:75–91DOI 10.1007/s10742-016-0153-9

http://orcid.org/0000-0002-1501-4152

http://crossmark.crossref.org/dialog/?doi=10.1007/s10742-016-0153-9&domain=pdf

http://crossmark.crossref.org/dialog/?doi=10.1007/s10742-016-0153-9&domain=pdf

1 Early years and graduate school

Juned: I was going to send you the questions ahead of time, but you once told me that

sometimes when you go into the studio, the first cut is the best.

Don: That’s right. Sometimes the spontaneity, you can’t recreate it. [Laughs.]

Juned: Don, tell me about your parents and your childhood. You were born and raised in

Chicago.

Don: Right. I grew up in Logan Square and then we moved to around Jefferson Park. My

parents were World War II war refugees. They were German. My mom was born in the

Crimea, my dad in Czechoslovakia. They got forced out of those areas as the war pro-

gressed, made it to Germany, stayed there for a few years, then came to the U.S. And then

they met here.

Juned: Those are neighborhoods on the Far Northwest Side of Chicago?

Don: Yes, on the Northwest Side of Chicago. Especially Jefferson Park. I went to grammar

school there, went to Lane Tech High School (Fig. 1), and then for college, I came here to

the University of Chicago.

Juned: You studied economics at the University of Chicago. How did you settle on

economics to begin with?

Don: I had no idea. I knew that I wanted to do something with math, but applied math, and

so it seemed like econ was like that. And then I took two micro econ courses and two

macro econ courses, and came to realize...eh, that’s really not what I like. But luckily the

econ degree allowed you take math classes as electives, so I only actually took five econ

courses and then supplemented that with a lot of math and then statistics courses, and I

found that that’s really what I liked.

Juned: And then did you go straight to graduate school at the University of Chicago?

Don: No, I graduated in 1980 and then spent a year working at Rush St. Luke’s Medical

Center in the Department of Psychiatry as a data analyst. I had taken as an undergraduate

about four or five stat classes, so I knew enough to do some basic statistics. So got a job

there and worked there for a year. During that year they brought Robert Gibbons on to be

Fig. 1 Don’s high school identification card from Lane Technical High School in Chicago

76 Health Serv Outcomes Res Method (2016) 16:75–91

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the Ph.D.-level statistician on a multi-site study on depression called the Collaborative

Depression Study.

I met Robert, and he told me about this program in quantitative psychology method-

ology at the University of Chicago and that they had the Thurstone Fellowship. He said I

should apply for that. At that time I was still thinking of maybe going into music as a

career, so I was playing in bands. But then I thought, well... So I did apply, and I was

always thinking of going back to graduate school, but not maybe so soon. I was thinking of

taking a few years off. But I got this fellowship and I thought gosh, if I can go to the

University of Chicago for graduate school for free, I can’t pass that up.

I remember the first time I met Darrell Bock, and he said you’ve just got to get

immersed in this, and I was like, ooh, I’m not so sure if I want to do that.

Juned: I’m in a band.

Don: Yeah, right, exactly.

Juned: Could you tell us a little bit about the Department of Behavioral Sciences,

Committee on Research Methodology and Quantitative Psychology?

Don: It was a small committee within Psychology. Bock, Don Fiske, those were the two

big names. Steve Shevell was there. I guess about four or five faculty altogether. So it was

a small group, which meant that we took courses in methodology. Bock taught courses on

multivariate statistics, on log-linear modeling, on item response theory. And Fiske taught

courses on research methodology—designing studies, evaluation research—so I took

courses like that. Shevell taught a class on mathematical psychology, and also one on

experimental design. That was another one within our committee. But there weren’t that

many, because it was a small group, so we were encouraged to take classes in statistics, in

econometrics, in other areas. And so I took a lot of courses, actually, in statistics at that

time.

Juned: And how much of your coursework was traditional psychology?

Don: Very little. In fact I never took a course like Intro to Psychology. We had to have a

substantive area, and I chose pharmacology because I was working in the Department of

Psychiatry as a data analyst, and I thought that it would make sense to learn their language.

So I took two, three, four classes in pharmacology, something like that. And learned a little

bit of pharmacology. So I’ve kind of learned psychology on the fly. It sort of mimics my

undergraduate career, in a sense, where I was an econ major, but I really didn’t take that

much econ.

Juned: Do you feel like it was a good choice to study quantitative psychology versus

something more traditional like statistics or biostatistics or even economics?

Don: You know, I’ve often thought about that. What was really good about quantitative

psychology was that because it was a small committee, we took classes in other areas,

whereas if I were strictly in a biostat program, I might not have done that. So the benefit

was I learned how sociologists applied statistics, how econometricians applied statistics,

how statisticians thought about statistics, how psychologists did, and I got exposed to, in

particular, latent variable models in psychology.

At that time—this was in the 1980s—there wasn’t that much exposure to latent variable

models of any type in statistics, per se. But in psychology, you can’t measure IQ or

personality with a blood test, right, so it’s all latent variables, really. And so is ability in

taking an educational test, that’s a latent variable. So I think that exposure really helped. In

fact, I learned a lot about latent variables, mostly from Darrell Bock... I guess pretty much

exclusively from him.

Juned: What was working with Darrell Bock like? Because he was your advisor, is that

right?

Health Serv Outcomes Res Method (2016) 16:75–91 77

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Don: Yes, he was. And I took several classes with him, and I was his TA for several of his

courses afterwards. He had a very high standard, which was good. He didn’t hold your

hand. I remember one of the first projects. He was working on mixed models and he knew I

had somewhat of a programming background, having taken math classes in numerical

analysis and programming in college, so he just says, program a mixed model. And so I had

to do this in Fortran and it was good to have that kind of independence.

I got to know him better when I was working on my dissertation. When you’re just

taking the classes, he was a bit aloof in some ways. But working on the dissertation, I

would meet with him regularly and he would point me in the right direction and give me

good ideas. But, you know, it was very much...he guided you, but you had to do it yourself.

Juned: This is the early ’80s. Is it fair to say Darrell Bock is kind of the father of modern

item response theory?

Don: I would say so. When he was working on his research, classical test theory was all

about basically the properties of a test. The problem with that is, you take one item off the

test, you have to regenerate the properties of the test. So he came to realize it’s better to

have a theory about items, not about tests, per se. And so he really developed IRT models.

And back then it was kind of interesting. Here in education, Ben Wright was here, and

he was a firm believer of the Rasch model, which is a one parameter IRT model, and

Darrell had developed the two parameter model, and the two...[Laughs.] So it seems kind

of weird these days, if you think about it, but...some debates are never settled!

Juned: Well, the one-parameter model is a special case of the two-parameter model.

Don: Exactly. That’s our point of view, right? But people who believe in the one-pa-

rameter model, they don’t see it that way. And I would say it’s true, if you design a test, if

it can satisfy the assumptions of the one-parameter model, there are certain benefits. But

the problem is, that’s hard to do sometimes, because the one-parameter model assumes that

basically all items have equal factor loadings. And that’s a very restrictive assumption.

Juned: The two parameter model, it has one parameter for the difficulty of the test?

Don: Right.

Juned: And then one for the discrimination of the test, is that right?

Don: Right.

Juned: And then the one parameter model would just have a parameter for the...

Don: The difficulty. And the difficulty is essentially how many people get this question

correct or not. That’s all it is, more or less. The discrimination is what says if the item is a

good discriminator between people of high ability or low ability. Again, it’s the factor

loading. So it can identify items that are kind of useless. Oftentimes what you see is that

items that are frequently endorsed or, you know, they’re close to the ends of the tail,

they’re bad discriminators, because they’re close to constants.

Juned: There are connections between some of these IRT models and mixed effects

models. For example, the Rasch model is a random intercept logistic regression model.

Don: Right, exactly. That was kind of interesting when I was working on mixed models in

the ’90s and came to realize, wow, I can estimate IRT models using mixed-effects soft-

ware. Obviously the way they parameterize things are different.

In IRT, the difficulty parameters, are centered around zero, essentially, and they make

the discrimination parameters basically multiplicatively centered around one. So they have

a nice interpretational quality. And in the mixed model you typically don’t do that. So I

worked on a book chapter once that kind of showed the connections between the two types

of models (Hedeker et al. 2006a). And basically, if you have mixed model software for

categorical data, you can essentially estimate, usually, many IRT models.

Juned: Can you talk a little bit about your dissertation work?


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Don: Sure. While I was a graduate student, I was also working, in the 1980s, as a research

assistant under Robert Gibbons in the Department of Psychiatry at the University of Illinois

at Chicago (UIC). And we would have a lot of studies with repeated measures, and they

often had missing data because they’re on humans, right? Back then the classical

approaches for dealing with repeated or longitudinal data were the analysis of variance

(ANOVA) approach or the multivariate ANOVA (MANOVA) approach.

Now, the ANOVA approach assumes compound symmetry for the variance-covariance

structure, and that’s rarely met. The MANOVA model doesn’t allow people with

incomplete data into the analysis, so they both have what I think are huge Achilles’ heels.

So I got interested in mixed models. And at that time Laird and Ware published their

seminal paper—this is like ’83, I think.

Juned: And that was for just linear mixed effects.

Don: Right. And Darrell had done a chapter (Bock 1983)—and this is when I was pro-

gramming some of that for him—on a similar sort of model. And so I got excited about this

area of research. And I did my dissertation on a linear mixed model with autocorrelated

errors (Hedeker 1989). And part of that was from my econ background, I guess, the

autocorrelated errors. I came to realize in a linear mixed model you’re assuming that errors

are independent. Well, they might not be independent.

Juned: Independent conditional on the random effects.

Don: Right, conditional on the random effects, exactly. Conditional independence

assumption. So I thought about introducing autocorrelated errors, and so in my dissertation

I put in AR1 errors. Also there was a non-stationary AR1 form that I put in there. And I

worked out the equations for that, did the programming for that, did a data analysis, did

simulations. And then I had one chapter additionally on ordinal mixed models, but I didn’t

program that. My initial intention was to do both. But after I had done so much work on the

continuous case, Darrell felt that was enough. So I defended in February of ’89.

In March of ’89, in JASA, there was a paper by Chi and Reinsel on linear mixed models

with AR1 errors (Chi and Reinsel 1989). My first thought was, thank God I defended last

month. My second thought was oh no, what am I going to do now? So that’s what kind of

then drew my attention more to the ordinal and categorical outcomes, and this work was

largely based on Robert’s work on mixed models for longitudinal binary out-

comes (Gibbons and Bock 1987). Which was a big influence on my work.

Juned: You said Darrell was also interested in mixed effects models. What were his

contributions?

Don: He wrote a book chapter in the early ’80s called The discrete Bayesian (Bock 1983).

It was essentially a linear mixed model. He showed how you can estimate it with an EM

algorithm. So it was pretty similar to Laird and Ware, but it was in a book chapter. It was

around the same time. And then in ’89 he had a collection called Multilevel Analysis of

Educational Data (Bock 1989). Looking over there, I have it on my bookcase. And so that

also had stuff about mixed models.

And it kind of grew. Darrell once told me, being in academics, it’s kind of like playing

bridge. You want to have a few possibilities, so if this works out, you go down this route. If

that works out... And his many students reflect this.

There are some that have gone the IRT route, like David Thissen and Bob Mislevy.

There are some that have gone into judgment and choice models, like Ulf Bockenholt.

There are some that have gone into multivariate statistics, myself and Robert Gibbons,

though Robert has done work in many areas. For human growth models, Eisuke Segawa

and Peggy Chandler. Adaptive quadrature solutions was Steve Schilling. I’m probably

forgetting a few, but obviously Darrell had his hands in many different places. But really,


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much of that was involved in some way or another with random effects or latent variable

models.

Juned: There were some other well known statisticians at the University of Chicago at that

time: David Wallace, Paul Meier, Raghu Bahadur, William Kruskal. Did you have any

interactions with them?

Don: I had several classes with David Wallace. Also with Ron Thisted I had several

classes. In fact he had a couple classes on programming and computation, so I took those

classes. And with Paul Meier, I remember this. When I was in college, when I was

finishing up my degree, I applied for a job at the National Bureau of Labor Statistics and I

had to have a signature from the department head basically saying that I had taken enough

classes or something like that.

Well, in those days, I was a pretty outlandish dresser, so I was dressed up in this military

jacket, and a leopard skin belt or something like this, and Paul Meier was like wow, that’s a

great outfit. [Laughs.] He was more impressed with my fashion than my statistical abilities,

no doubt. So I think the people I took the most classes with were certainly David Wallace

and Ron Thisted.

Juned: I should have asked this question earlier. What’s the status of the Committee on

Research Methodology and Quantitative Psychology? Is it still around?

Don: No. It’s kind of sad because a lot of good people went through it. But when Fiske

retired, and then when Darrell Bock retired, they didn’t seem to hire people, so it seemed

like it died out. I think Eisuke Segawa was maybe the last graduate from that committee. I

was close to the last, but not the last.

Juned: You weren’t the reason that it died out?

Don: No, it wasn’t me. Don’t blame me for this. Although one time I remember, Darrell

had his CV online somewhere, and it listed all his graduate students, and I wasn’t on the

list, so I was thinking... is he trying to tell me something? I contacted him and he put me on

the list. So it wasn’t a purposeful slight—I was relieved.

Juned: You mentioned Robert Gibbons already a few times, and how you began working

with him at Rush. Could you talk about your relationship and how that started and how it’s

grown or continued?

Don: I met Robert when I was working right after college at Rush as a data analyst. And he

had just finished his Ph.D. here under Darrell, and he was the statistical supervisor on the

study, and he would tell me things to do, and I would do them. And as soon as I met him I

was like wow, I want to know everything that guy knows. Because he is so brilliant, and he

can explain things so well.

The thing with Robert that distinguished him from some of the other people I had been

exposed to was he could really communicate with the psychiatrists and make them

understand some advanced statistical concepts in a pretty clear way. And I thought that was

an amazing talent he had, and so I wanted to learn more about that. So again, he told me

about this program at U of C, so I applied to that, got that. And then I was working for him

basically.

Juned: And so you continued to work with him throughout grad school?

Don: I worked with him throughout grad school and he was on my dissertation committee.

Both him and Darrell were and are my mentors. I’ve learned everything from them, and

wouldn’t be here if not for them, but don’t blame the teachers for the mistakes of the

student! And then after grad school I continued to work with Robert through the years. It’s

been an amazing collaboration that changed my life (Fig. 2).

Juned: You began working at UIC after you graduated?


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Don: Right after I graduated in ’89 there weren’t really too many jobs in psychology, or

the kind of jobs that were around were ones where they wanted you to teach the quant

courses, but they wanted you to have a substantive area in psychology, and my area was

methodology. And I also wanted to stay in Chicago, primarily for my musical reasons. And

so I continued working at UIC under Robert in Psychiatry, but didn’t get a faculty job until

’93, when something opened up in Biostatistics in the School of Public Health at UIC. I

applied for that job and got it.

Juned: So when you graduated in ’89, you had kind of a research position?

Don: Right. I forget what the title was. Research Specialist or something like that. In ’91 I

started working at what was called the Prevention Research Center. I was half there and

half in Psychiatry with Robert. The Prevention Research Center was led by Brian Flay and

Robin Mermelstein. These are people that I then started to collaborate with. It’s now IHRP.

What does it stand for? I don’t know.

Juned: Institute for Health Research and Policy.

Don: That’s it, right.

Juned: I did my research.

Don: Yes, you did. So I’m still connected with that place, and I started there in ’91

working with Brian Flay and Robin Mermelstein, and I continue to work with Robin in the

area of smoking.

2 Music

Juned: Music has been a big part of your life for a long time. Could you talk about your

interest in music, how it began, and your current band, the Polkaholics?

Don: I was one of those kids that grew up in the ’60s, and I saw the Beatles on the Ed

Sullivan Show when I was 5 or 6 years old and I thought, wow! It just blew my mind. It

was like, I want to get a guitar. As soon as I saw that, I wanted to sign up. But it took until I

was about ten till I finally did get a guitar, and then I started taking lessons at the YMCA

Fig. 2 Don and Robert Gibbons in 1989 at Don’s Ph.D. graduation from the University of Chicago


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and things like that. And then when I was in high school I started playing in bands, and so

I’ve been playing...

Juned: Rock?

Don: Rock bands. Back in those days, we would play cover songs. By high school I got

really into the Rolling Stones, and I was trying to learn all the Rolling Stones songs I could,

and bands like that. So that’s the kind of bands I was in in high school. We played at sock

hops and high school events. My first performance was this. We played a Sadie Hawkins

dance. Do you know what a Sadie Hawkins dance is?

Juned: That’s when the girls ask the boys.

Don: Right, right! At Taft High School, which was my neighborhood high school. I had

gone to Lane, but all of my friends that I had gone to grammar school with were at Taft. So

we play at Taft. A lot of these people I knew from grammar school were there. We were

terrible. I was so nervous, on my amplifier, I turned up the volume, but turned up no treble,

bass, or mid, so the sound was really weird. At one point they actually pulled the electrical

plug on us. I’m not kidding you. [Laughs.]

We were awful. We played and then they had a professional sock hop band playing.

And they even said this. They said we’re going to play Smoke on the Water the way it’s

supposed to be played. [Laughs.] Ouch. Big time ouch. But, you know, when you fall on

your face, you’ve got to get up, so I got up and continued. So anyway, I continued with

bands. I played in bands here at the University of Chicago. My biggest musical claim to

fame is in spring of 1980, when I was a senior here at U of C, they had the Ramones

playing at Ida Noyes Hall, and we got to open for the Ramones.

Juned: Oh, wow!

Don: Right, right. At that time, I was in a band called the Trouble Boys (Fig. 3). We

played events here at U of C. We had a mix of cover songs and original songs. So that’s

when I first started writing songs, with that band. I had a few songs, the bass player had a

few songs, and then we did covers like cheesy ’60s songs like ‘‘Secret Agent Man,’’ ‘‘I’m

Not Your Stepping Stone,’’ things like that.

And there’s this great photo from that event. The Ramones had these big amps. We had

these little puny amps. The photo shows us on stage, and all you see is us with those big

amps in back of us. We looked like a real rock band. And then in the ’80s I was in a poetry

musical band called Algebra Suicide. That was with the poet Lydia Tomkiw. We went to

Europe twice with that band. We seemed to have more popularity in Europe.

Juned: What kind of band was it?

Don: So the way it started was, I was playing in bands and Lydia Tomkiw was a poet. And

so we thought of trying to combine our art forms. And so we did. When we began, we used

a drum machine, because in the ’80s drum machines were kind of popular. But also we

could not...there’s no way we could have had a real drummer because always the issue with

that was to play music in such a way that you could still hear every single word that she

said. And she’s not singing, so the volume that’s coming out is not like a singer.

So when we began, it was pretty minimal. It was just me on guitar with a drum machine

and her reciting poetry. And over the years it got a little bit more elaborate musically. I

then started playing around with synthesizers and then putting stuff on a backing tape, and

then playing guitar over this backing tape that had synthesizers and drums, and then she

would still recite.

And she developed this whole audiovisual thing where she made handmade slides with

different colors and would project them onto us, so it was a bit like a performance art kind

of thing. And that continued from, I think, in ’82 or thereabouts and went to ’92 or

something like that, and we released, I don’t know, three, four, five CDs, something like


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that. At that time it was important for us, and we had some success. We played in New

York, at The Knitting Factory. [Laughs.]

Juned: Before the Polkaholics, were those your first releases?

Don: Yeah. The first thing I ever released. With the Trouble Boys, we never released

anything. Then I was in a band called The Pajamas and then Psycho Capones after that.

That was a band where we tried to dress like gangsters. It was kind of a fun thing. But

anyway, with Algebra Suicide we first put out seven inch records, and then eventually it

got to cassette tapes, and then to CDs.

Then, after that broke apart, I had a rock band called Bouncing Balls that was around for

a little bit. We released a CD. Some of that material was actually stuff I had written with

the Trouble Boys. And then eventually I started the Polkaholics (Fig. 4). And how I started

the Polkaholics was this. It’s kind of a long story. When I was in high school, I played in a

band where we played a couple weddings. And if you play a wedding in Chicago, you have

to play a Polka song.

Juned: That gets everyone on the dance floor.

Fig. 3 The Trouble Boys in 1979 (left to right): Larry Cohen, Bart Goldberg, Mark Erwin, MichaelHaederle, Don Hedeker


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Don: You gotta do it. I remember learning ‘‘Beer Barrel Polka’’ and one other, and I was

like, wow, this is kind of cool, actually. That was my impression back when I was in high

school. And then it kind of stopped there.

Juned: You kept that to yourself, though. You can’t tell your friends you’re a Polka fan

when you’re in high school.

Don: Right. No, no, no, no, definitely not. And then, you know, in the ’90s, me and my

wife Vera, we went to thrift stores a lot to get outlandish clothes, and eventually my closet

got completely filled, I couldn’t fit any more clothes, so I started looking at the records.

And I saw these Polka records, and it just kind of intrigued me, so I started buying them.

And I had no idea about Polka music. I thought there’s like 100 Polka songs.

I had been exposed to the Lawrence Welk Show and thinking like oh, this is the nerdiest

music ever. And then I started getting these records and realizing wow, this is really wild

music. I always tell people it’s like imagine if the only rap you had ever heard was Vanilla

Ice. That’s kind of like what the Lawrence Welk Show is for Polka, in a way. Once you

start digging, you see that this music’s got a lot more vitality. It’s just a lot wilder than that.

Juned: Your parents were German. Were there any Polka records around the house?

Don: There were, but mostly the German style. My mom played accordion when I was

growing up, so I got exposed to that. And of course I was—yeah, I tell people this, too—

it’s like when I was growing up, I didn’t want to be on Hogan’s Heroes, I wanted to be on

the Brady Bunch. I didn’t want to be German, I wanted to be American. I think every first

generation kid feels this way. But then later on in life you come to realize that ethnic

identity is important and it’s useful.

You know, Iggy Pop, he once said he had to find his own Blues, and I felt that way, too.

I’ve got to find my own music. And so to me Polka connected with my ethnic background

and growing up in Chicago, and so I thought, wow, maybe we can play this music with our

standard rock instrumentation. So when we started, it was just like can we even pull this

off. And we did, and it was like wow, this is so much fun. So 18 years later, here it is, and

we’re still going.

Fig. 4 The Polkaholics at the May Fest in Lincoln Square in 2014. From left: Blitz Linster on bass andvocals, Action Jackson on drums and vocals, and Dandy Don Hedeker on guitar and vocals


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Juned: How has music influenced your research, and how has your research influenced

your music? How do you put it all together? Is it the weekdays for research, weekends for

music?

Don: I often think that being in a band and having that side of things has made me a better

presenter. Like anyone, when you first perform or first give a lecture, you’re nervous. But

having done this so many times, and learning how to engage an audience, that’s helped my

presentation style, I think, in statistics. When you’re doing either one you’re trying to

engage the audience. One obviously is a little bit less intellectual than the other. But there

are aspects of performance in giving a lecture.

Juned: And in a statistical talk, if you entertain your audience, they learn more and they

remember more.

Don: Precisely. And that was another thing that I picked up from Robert Gibbons. The first

time I heard him give a lecture, it was like wow, this guy’s the best lecturer I’ve ever heard.

He was just so good. So I wanted to learn how to do that. And then people maybe think I

was a natural or whatever. That’s not the case. When I first gave lectures, I was bad. When

I first wrote articles, I was bad.

But I really worked on those things because I felt communication, both oral commu-

nication and written communication, are so important in academics. With written com-

munication, what I remember is being an undergraduate and going in the stacks at

Regenstein Library and seeing some books by Milton Friedman, and I thought, I’m just a

lowly undergraduate in econ, I’ll never understand this. And I opened it up and I was like

wow, this is really clear. And came to realize clarity in presentation, either orally or

written, is so important.

And a lot of what it revolves around is, I think in oral, is practice. When I would first do

my lectures at conferences, I would practice them before doing it. And I tell the graduate

students, practice this in front of your wife or husband, whoever, in front of an audience.

That’s orally. Written it’s editing. It’s like reread it, rewrite it.

A lot of the students in biostatistics are foreign born and they think that I can just write

things down and it’s perfect, but that’s not the way it is. You have to rewrite it and always

look to improve in terms of the clarity of expression. That’s so key, really.

Juned: And how do you fit music into your life?

Don: So how I fit it in is...it’s a juggling act. Nowadays we play shows maybe like once or

twice a month. We practice about once a week. So it’s not too overwhelming. Before I had

my daughter, I had two bands going.

Juned: You do now, too.

Don: That’s true. The Imposteriors, the Bayesian band led by Brad Carlin. You’re right. So

how that happened, a couple years ago I co-hosted the International Conference on Health

Policy Statistics (ICHPS) here in Chicago with Andrew Zhou. And as part of that, we

wanted to have an entertainment thing, so I thought, well, I’ll have the Polkaholics play at a

venue. And then I knew Brad was a musician, because sometimes in AMSTAT News you

would see a photo of him playing music. He played at various conferences, like the

Bayesian conferences.

And I knew Brad, so I emailed him and asked him if he wanted to join the band for

some songs, and he was up for it, and it was fantastic. He’s such a great musician, it’s

unbelievable. He sings so well, plays incredibly well. So that was so much fun having him

join the Polkaholics for the ICHPS show. And then he asked me to play in The Impos-

teriors for a talent show the ASA had in Boston 2 years ago for the Joint Statistical

Meetings.


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And so we played one song for the talent show, ‘‘Bayesian Believer,’’ which is the

Monkees ‘‘I’m a Believer’’—actually Neil Diamond ‘‘I’m a Believer.’’ And so we played

that, and it was a blast. Jennifer Hill, a great singer, Mark Glickman on bass, fantastic bass

player, Michael Jordan, terrific on drums. Just a topnotch group of people (Fig. 5).

Juned: Actually, topnotch statisticians, too.

Don: Yeah, no kidding. I know. I was like, wow!

Juned: If the music doesn’t work out...

Don: We’ve got a day job. [Laughs.] But it was so much fun. So then Brad got ASA to

allow us to play the full night at JSM in Seattle for the mixer or whatever it is, the social

event. We had to learn three sets of material. And so when he first talked to me about this I

was thinking, oh, we’re going to play stuff like ‘‘Louie, Louie’’ three chord rock songs,

simple things. No, no. The material, some of it was rather challenging. So we practiced

through the Internet several times before finally getting together in Seattle and practicing

face-to-face, and that went well. And then we played more recently at the ICHPS con-

ference in Providence, and now our next gig is...we might play at the Causal Modeling

Conference.

Juned: How about that!

Don: [Laughs.] It’s turning into a whole other thing. But it’s so much fun playing with

them, it’s just a blast.

3 Research

Juned: While at UIC you were affiliated with the Institute for Health Research and Policy.

Could you talk about your work there and your collaborations with Robin Mermelstein? It

seems like a lot of your ideas for statistical work come from these collaborations.

Fig. 5 The Imposteriors at the 2015 JSM in Seattle. From left: Brad Carlin, Jennifer Hill, Michael Jordan,Don Hedeker, Mark Glickman


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Don: Exactly. I started working with Robin Mermelstein, who’s a psychologist in 1991.

Her and Brian Flay. I was working on both of their projects. And a lot of their work was

about either smoking prevention, in Brian’s case, or smoking cessation in Robin’s case.

And I didn’t really know anything about those areas when I began, but I started working

with them. And it’s true that a lot of my research has developed out of that research.

I think collaboration, for a biostatistician, is really important because, throughout my

career, I’ve always tried to develop methods that can be used, and not some statistical thing

that nobody’s going to use. So when you deal with actual research in some substantive

areas, you come to learn how they’re doing things and how you can improve upon that.

So in smoking cessation studies back then, they would code missing values as missing

equals smoking. And I was thinking this is not the optimal way of handling missing data in

a smoking cessation study. So I worked on developments there, first using Robert’s mixed

model for longitudinal binary data (Gibbons and Bock 1987) in an outcome paper (Gruder

et al. 1993). This led to more papers on missing data in smoking cessation studies like -

Hedeker et al. (2007). Another thing I worked on with Robin was I had done this work on

ordinal mixed models coming out of my dissertation, and in areas of prevention research a

big thing is the Stages of Change Model. And that’s really an ordinal variable, and so I

came to develop models for data like that (Hedeker and Mermelstein 1998; Hedeker et al.

1999). I was also working on smoking cessation studies with Bonnie Spring who was at the

VA Medical Center and Lenny Jason at DePaul. I sort of became the smoking statistician

here in Chicago, I guess. And then with Robin more recently I’ve been working on

ecological momentary assessment (EMA) studies.

Juned: Those are studies where adolescent smokers are randomly prompted?

Don: Right. In those studies...well, they’re not all smokers, but a large majority are. In the

old days they would carry around a Palm Pilot for a week or so, and they would get

randomly prompted throughout the day, and they would answer various questions, like who

are they with, what’s their mood like. Mood was a big one. And then they would also,

when they smoked a cigarette, they would engage the device and basically answer some

more questions.

And so one big question is, are these adolescents smoking at times when their mood is

bad, and they want to get it to normal levels? Or are they smoking to enhance their mood?

And so I started to develop models for that. And then I came to realize that with 30, 40

measurements per week, we could do more than just model the mean structure.

And really it was my collaboration with Robin and Bonnie Spring and Lenny Jason that

led to this. I would hear them say, one reason that smokers say they smoke cigarettes is to

regulate their mood. And I thought regulation of mood isn’t about mean levels, per se, it’s

about variance. And with EMA data, we have this possibility of modeling the variance.

When I started working on this, I thought I was the only person in the world doing this.

And then I did some literature reviews and I see oh, there’s other people that are doing this

kind of stuff as well, and it’s kind of a growing thing. So I started working on methods to

allow the modeling of the mean and the variance, both the between subject variance and

the within subject variance in terms of covariates, and also having random effects in terms

of the variance (Hedeker et al. 2006b, 2008, 2009a, b).

All of this work, much of my statistical developments have been through collaboration

and trying to improve upon the methods that my colleagues are using, and trying also to

make methods that they can use.

Juned: A lot of the work is within the framework of random effects models. What is it

about that framework that’s so flexible that you can use it to address so many questions?


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Don: I guess it’s partly my graduate school training in psychometrics and psychology. In

those fields there’s so much interest in individual differences. That’s the whole focus,

really.

Juned: And latent variables.

Don: Right, right. And so that led to these random effect, these mixed models. So I’ve

really done most of my work in that area. Of course you come to some other areas, and

they don’t believe in random effect models, right? [Laughs.] I remember once I was talking

to a biostatistician—this is not that long ago—but he was asking me, oh, what’s your

research on. And I said random effect models for categorical outcomes. And he goes, oh, I

didn’t really even think that that existed. [Laughs.]

Juned: You spent 30 years at UIC. It’s uncommon these days for people to stay anywhere

for nearly that long. What was the reason for staying that long?

Don: A major reason for me staying in Chicago is my musical activities. I’ve developed

connections and networks that I couldn’t recreate if I went somewhere else. That’s an

important part of my life and something I want to continue, so that made me think about

Chicago very much. UIC was a good place for me in Biostatistics there.

When I first started at UIC, I had taught a course in the Psychology Department, a

statistics course, and the chairperson at that time said look, we’re going to have a search

next year, and so you might consider that. And actually, that was my plan, was to go into

Psychology there. But then, over the summer, an opening was in Biostat, and I thought, if I

don’t apply for this job, and I don’t get the Psych job, I’m going to be kicking myself. So I

applied for the Biostat job, got that, and I tried to convince them that even though I wasn’t

trained in biostatistics I would fit in there. And I think partly that was because most of my

substantive research was in psychiatry, mental health, and so that wasn’t that far of a

stretch. And so I started in ’93 in the School of Public Health and Biostatistics there.

At that time our department was largely collaborative biostatisticians, and we had

mostly just a training program, an M.S. in Biostat. We had just maybe a handful of Ph.D.

students. So that’s something that I felt there was an opportunity to try and develop the

department to get more biostat research going on, to get more graduate students, and so

that’s what I tried to do in my time at UIC. But then this opportunity developed here at the

University of Chicago, and of course I went to college here, I went to graduate school here.

It was just too good to pass up the opportunity to come back.

Juned: And some of the people who we were talking about whom you took classes from as

a graduate student, like Ron Thisted, they’re still here.

Don: Right. It’s weird for me to think of myself as a peer of his. When I was taking classes

with him, he was junior faculty at that time. He had just finished his Ph.D. at Stanford and

had come here. He was another great presenter, a great teacher, and it was people like him

that really inspired me to be a good teacher as well.

Juned: I’ve noticed that you’ve published as many methodological articles in substantive

journals as you have in statistical journals. Why do you do this?

Don: I feel it’s important, obviously, to develop methodology, but I also think it’s

important to try to disseminate that methodology and try to get people in psychology and

areas that I’ve worked in to have a better understanding of these methods. So I’ve pub-

lished several papers in, for example, Journal of Consulting and Clinical Psychol-

ogy (Hedeker et al. 1994, 1996).

Because that’s where you can have an impact, I think, is by getting your methods in the

hands of M.S. level statisticians who are working on research projects in substantive areas.

If you can get your stuff to them, you can have a big impact, or bigger.


123

Juned: And all you have to do is look at the citations of your articles, and they’re much

higher in the substantive journals, in general.

Don: It’s true. They can have a big impact, that’s for sure.

Juned: Is that the same motivation for writing software? Nowadays there are R packages

to help you write R packages. But 20 years ago when you started, you were doing it in

Fortran.

Don: Right. How that developed, it came out of my dissertation. For my dissertation I had

programmed a mixed model in Fortran. At that time there was no SAS PROC MIXED.

These things didn’t exist. And so Robert Gibbons, he put a grant in to NIMH to write

software for mixed model analysis, and so that led to us publishing and supporting

MIXREG for continuous outcomes (Hedeker and Gibbons 1996) and MIXOR for

dichotomous and ordinal outcomes (Hedeker and Gibbons 1996).

And again, the impetus was like...it’s great if you can do this analysis, but it would be

even greater if other people can do this. Fortran is considered a dinosaur language at this

time, but it’s still very fast. More recently I’ve written a program, MIXREGLS for location

scale modeling of EMA data (Hedeker and Nordgren 2013). I wrote that in Fortran. But I

figured out how you can get it to the R users, right? Because that’s changed so much. I’ve

been an Associate Editor at the Journal of Statistical Software for a long time, and in the

early days we would get submissions in various languages—Fortran, C??, SAS IML, all

kinds of things. Now everything that comes in—or much of what comes in—is R. So that’s

where things have gone. And like you say, it’s almost like there’s so many R packages, it’s

overwhelming.

Juned: And the other thing is reproducibility. If you can release a software package,

people can reproduce your results. And you can use the software yourself for your own

research, too.

Don: Right. The other thing with doing software, it helped me to understand these methods

to a much greater extent, in many ways. One is in writing it, writing the code, but also in

releasing the software. I would get users that would say hey, I tried your software out, it

doesn’t work. So I’d say send me your data and then I’d see why it wasn’t working. So I

came to learn a lot of lessons that I would not have learned otherwise. So developing

software has helped me enormously, to understand the methodology and the interpretations

and things like that.

Juned: You and Robert wrote a book on longitudinal data (Hedeker and Gibbons 2006).

How did you decide to do that?

Don: It came out in 2006, but we had it in our mind to do it in the late ’90s, and we actually

submitted a proposal to an unnamed book publisher who rejected it. [Laughs.] It’s like I

always tell my students, everybody gets rejected. It’s how you react to the rejection that

counts. Everybody gets rejected. So that got rejected.

But then we went to another publisher. Eventually our proposal was accepted by Wiley,

and we started to work on it. When we first started it there really wasn’t too much out there

in terms of good books on longitudinal data. Now, of course, there are several very good,

excellent books on longitudinal data in different areas.

Again, the idea is to disseminate and try and present the methodology in a way that’s

not overwhelming technically. It’s a fine line you’ve got to walk. You don’t want to make

it so simple that you lose meaning. So trying to strike that right balance.

Juned: I have a bunch of longitudinal books, but that’s the first one I always turn to.

Don: Oh, really? Well, that’s very nice of you.


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4 Future

Juned: What does the future hold for you? Do you have any ongoing projects underway or

new methodological areas?

Don: Yes, definitely. I have a grant from NHLBI with Genevieve Dunton from the

University of Southern California to further develop the software that we’ve been working

on for mixed location scale models. So in the software that I first put out, it just has a

random intercept in terms of the mean and a random intercept in terms of the variance.

More recently what I’ve developed is to allow multiple random effects in terms of the

mean, so intercept and trend, things like that. You have multiple random effects there, and

then to build a second model where the random effects from the first model influence a

subject’s outcome. So that was the nature of the grant, and we’re working on methodology

for that. And that’s going well.

Of course another thing I want to work on is...I did a paper on location scale models for

ordinal data, but I did that with SAS NLMIXED. So I’d like to extend my MIXOR program

to also have random scale parameters. So further developing the methodology I’ve been

working on for intensive longitudinal EMA data would be what I hope to accomplish.

Juned: Are there any other topics we should talk about or you want to mention?

Don: I’m obviously flattered to be interviewed and to get this long-term excellence

award (Fig. 6). It makes me feel like an old person [Laughs.] But I guess having thought

about it, it’s like, wow, yeah, I guess I’ve been around for a long time.

Juned: Well, certainly lots of excellent work going back.

Don: Thanks. That’s so nice. The other thing is, I’ve done so many presentations, work-

shops. And again, it’s trying to get the message out there to people to help them use these

methods in their own research. And it seems to me that’s how statistics can advance, is the

more people know about these methods, the more they can utilize them in their own work.

This hopefully helps science in many areas.

Fig. 6 Don in October 2015 receiving the Health Policy Statistics Section Long-Term Excellence Awardfrom Susan Paddock in Providence, RI


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Juned: Well, for me, one of the great thrills of my career has been the opportunity to work

with you.

Don: It’s so nice of you to say that, because when we’re on those conference calls, I’m

always thinking what would Juned say about this. You keep me honest, too. [Laughs.]

Juned: Thank you, Don.

Don: Thank you.

Compliance with ethical standards

Conflict of interest The author has no conflicts of interest to disclose.

Ethical approval This article does not contain any studies with human participants or animals performedby any of the authors.

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