QuestionsQuestions

What is the best way to avoid order effects while doing What is the best way to avoid order effects while doing within subjects design?within subjects design?

We talked about people becoming more depressed during We talked about people becoming more depressed during a treatment period, but would a history effect also include if a treatment period, but would a history effect also include if a participant became happier due to an outside factor other a participant became happier due to an outside factor other than the treatment being done?than the treatment being done?

What is an example of participant attrition?What is an example of participant attrition? When a study is being conducted, if a confounding variable When a study is being conducted, if a confounding variable

was found, would the study make changes to control the was found, would the study make changes to control the confounding variable right away, or would they continue the confounding variable right away, or would they continue the study but note the confounding variable in the discussion?study but note the confounding variable in the discussion?

More QuestionsMore Questions

How do you determine how much time should pass How do you determine how much time should pass between treatments to ensure that your counterbalancing is between treatments to ensure that your counterbalancing is effective?effective?

I really don’t understand counterbalancing. Can you explain I really don’t understand counterbalancing. Can you explain it in a really simplistic way?? Why would you use this it in a really simplistic way?? Why would you use this method?method?– Two groups going through the same treatments in different order – Two groups going through the same treatments in different order –

it is still a within subjects designit is still a within subjects design Does counterbalancing eliminate order effects?Does counterbalancing eliminate order effects? In matched-subject designs is the matching randomly In matched-subject designs is the matching randomly

assigned even though researchers are matching assigned even though researchers are matching participants based on certain characteristics?participants based on certain characteristics?

More QuestionsMore Questions

Is it possible to use other statistical analyses such as Is it possible to use other statistical analyses such as regression, Chi-square, F-test etc. rather than ANOVA and regression, Chi-square, F-test etc. rather than ANOVA and t-test in within-subjects or between-subjects designs?t-test in within-subjects or between-subjects designs?– Regression – determines function of the best fit to your data Regression – determines function of the best fit to your data

(relationship between dependent and independent variables)(relationship between dependent and independent variables)– Chi-square – data consisting of proportionsChi-square – data consisting of proportions– F-test (ANOVA) – t-test (two groups) as a special form of F-test F-test (ANOVA) – t-test (two groups) as a special form of F-test

(more than two groups)(more than two groups)– Analysis of covariance – ANCOVAAnalysis of covariance – ANCOVA– Multivariate analysis of variance - MANOVAMultivariate analysis of variance - MANOVA

Can the final be open notes? I wrote out all the key words, Can the final be open notes? I wrote out all the key words, did all the exercises etc. I can’t memorize like that. Are you did all the exercises etc. I can’t memorize like that. Are you going to curve?going to curve?

Nonexperimental and Quasi-Nonexperimental and Quasi-Experimental Strategies: Experimental Strategies:

Nonequivalent Group, Pre-Post, Nonequivalent Group, Pre-Post, and Developmental Designsand Developmental Designs

Chapter 10Chapter 10

Dusana RybarovaDusana RybarovaPsyc 290B Psyc 290B

May 26 2006May 26 2006

1. Introduction1. Introduction

quasi-experimental research strategyquasi-experimental research strategy– like an experiment, typically involves a comparison of like an experiment, typically involves a comparison of

groups or conditionsgroups or conditions– however, it uses a nonmanipulated variable to define however, it uses a nonmanipulated variable to define

groups or conditions being compared such as age, groups or conditions being compared such as age, gender or time (before vs. after treatment)gender or time (before vs. after treatment)

– within the context of quasi-experimental research, the within the context of quasi-experimental research, the variable that is used to differentiate the groups of variable that is used to differentiate the groups of participants or the groups of scores being compared is participants or the groups of scores being compared is called the quasi-independent variable (e.g. age)called the quasi-independent variable (e.g. age)

– the variable that is measured to obtain a score for each the variable that is measured to obtain a score for each individual is called the dependent variable (e.g. IQ individual is called the dependent variable (e.g. IQ score)score)

1. Introduction1. Introduction

Nonexperimental research strategyNonexperimental research strategy– Very similar to quasi-experimental research Very similar to quasi-experimental research

strategystrategy– Major distinction – nonexperimental designs Major distinction – nonexperimental designs

make little or no attempt to minimize threats to make little or no attempt to minimize threats to internal validityinternal validity

– Just like in the quasi-experimental designs there Just like in the quasi-experimental designs there is no real manipulation of variables is no real manipulation of variables

– In contrast to quasi-experimental designs there In contrast to quasi-experimental designs there is less rigor in control of extraneous variablesis less rigor in control of extraneous variables

1. Introduction1. Introduction

in what follows we will use the following in what follows we will use the following symbolssymbols

X – represents the treatment X – represents the treatment O – represents an observation or measurementO – represents an observation or measurement

– 2 groups of nonexperimental and quasi-2 groups of nonexperimental and quasi-experimental designs:experimental designs: Between-subjects designs or nonequivalent group Between-subjects designs or nonequivalent group

designs designs Within-subjects designs or pre-post designsWithin-subjects designs or pre-post designs

2. Nonequivalent group designs 2. Nonequivalent group designs (between-subjects)(between-subjects)

nonequivalent group design is a research study in nonequivalent group design is a research study in which the different groups of participants are which the different groups of participants are formed under circumstances that do not permit the formed under circumstances that do not permit the researcher to control the assignment of individuals researcher to control the assignment of individuals to groups because those groups are pre-existing; to groups because those groups are pre-existing; the groups of participants are therefore considered the groups of participants are therefore considered nonequivalentnonequivalent

e.g. a researcher wants to evaluate a teen e.g. a researcher wants to evaluate a teen pregnancy prevention program by comparing the pregnancy prevention program by comparing the pregnancy rates in a high school where the pregnancy rates in a high school where the program is used with pregnancy rates in a high program is used with pregnancy rates in a high school that does not use the programschool that does not use the program

2. Nonequivalent group designs2. Nonequivalent group designs

nonequivalent group design has a built-in threat to nonequivalent group design has a built-in threat to internal validity that precludes an unambiguous internal validity that precludes an unambiguous cause-and-effect explanation, i.e. assignment biascause-and-effect explanation, i.e. assignment bias

three examples of nonequivalent group designsthree examples of nonequivalent group designs– the differential research design (nonexperimental)the differential research design (nonexperimental)– the posttest-only nonequivalent control group design the posttest-only nonequivalent control group design

(nonexperimental)(nonexperimental)– the pretest-posttest nonequivalent control group design the pretest-posttest nonequivalent control group design

(quasi-experimental)(quasi-experimental)

2. Nonequivalent group designs2. Nonequivalent group designs the differential research design (nonexperimental)the differential research design (nonexperimental)

– simply compares pre-existing groupssimply compares pre-existing groups– uses a participant characteristic such as gender, race, or uses a participant characteristic such as gender, race, or

personality to automatically assign participants to groupspersonality to automatically assign participants to groups– no random assignment of participants to groupsno random assignment of participants to groups– dependent variable is then measured for each participant to dependent variable is then measured for each participant to

obtain a set of scores within each groupobtain a set of scores within each group– the goal of the study is to determine whether the scores for one the goal of the study is to determine whether the scores for one

group are consistently different from scores in another groupgroup are consistently different from scores in another group– e.g. mother’s and father’s involvement in the peer relationships e.g. mother’s and father’s involvement in the peer relationships

of their adolescent childrenof their adolescent children– in differential research, participant differences in one variable in differential research, participant differences in one variable

are used to create separate groups, and measurements of the are used to create separate groups, and measurements of the second variable are made within each groupsecond variable are made within each group

– correlational study treats all the participants as a single group correlational study treats all the participants as a single group and simply measures the two variables for each individual and simply measures the two variables for each individual

2. Nonequivalent group designs2. Nonequivalent group designs

Post-test only nonequivalent control group Post-test only nonequivalent control group design (nonexperimental)design (nonexperimental)– compares two nonequivalent groups of participantscompares two nonequivalent groups of participants– one group is observed (measured) after receiving a one group is observed (measured) after receiving a

treatment, and the other group is measured at the treatment, and the other group is measured at the same time but receives no treatmentsame time but receives no treatment

– Does not protect agains assignment biasDoes not protect agains assignment bias– e.g. the teen pregnancy programe.g. the teen pregnancy program

X OX O (treatment group)(treatment group)

OO (nonequivalent control group)(nonequivalent control group)

2. Nonequivalent group designs2. Nonequivalent group designs Pretest-posttest nonequivalent control group Pretest-posttest nonequivalent control group

design (quasi-experimental)design (quasi-experimental)– compares two nonequivalent groupscompares two nonequivalent groups– one group is measured twice – once before a one group is measured twice – once before a

treatment and once aftertreatment and once after– Problem of assignment bias even though it is reduced Problem of assignment bias even though it is reduced

by pre and post measurementby pre and post measurement– Potential problems with differential history effects, Potential problems with differential history effects,

differential instrumentation, differential testing effects, differential instrumentation, differential testing effects, differential maturation and differential regressiondifferential maturation and differential regression

– the other group is measured at the same two times the other group is measured at the same two times but does not receive any treatmentbut does not receive any treatmentO X O (treatment group)O X O (treatment group)

O O (nonequivalent control group)O O (nonequivalent control group)

3. Pre-post designs (within-subjects3. Pre-post designs (within-subjects))

series of observations is made over time on one group of series of observations is made over time on one group of subjectssubjects

Internal validity is threatened by time-related effectsInternal validity is threatened by time-related effects

one-group pretest-posttest design (nonexperimental)one-group pretest-posttest design (nonexperimental)– Each individual in a group is measured once before and once after Each individual in a group is measured once before and once after

a treatmenta treatment– Does not control for possible extraneous variables possibly causing Does not control for possible extraneous variables possibly causing

change over timechange over timeO X OO X Oe.g. evaluating the effectiveness of a new political TV commerciale.g. evaluating the effectiveness of a new political TV commercial

3. Pre-post designs (within-subjects)3. Pre-post designs (within-subjects) time series and interrupted time-series designs time series and interrupted time-series designs

(quasi-experimental)(quasi-experimental)– Series of observations for each participant before a Series of observations for each participant before a

treatment and a series of observations after the treatment and a series of observations after the treatmenttreatment

– Eliminates many problems with the pretest-postest Eliminates many problems with the pretest-postest design, outside events are a confound only if they occur design, outside events are a confound only if they occur simultaneously with the treatmentsimultaneously with the treatment

O O O X O O OO O O X O O O– Time series design – treatment administered by the Time series design – treatment administered by the

researcherresearcher e.g. anger management program for studentse.g. anger management program for students

– Interrupted time-series design – event or treatment is Interrupted time-series design – event or treatment is not created by the researchernot created by the researcher e.g. legal changee.g. legal change

3. Pre-post designs (within-subjects)3. Pre-post designs (within-subjects) Equivalent time-sample design (quasi-Equivalent time-sample design (quasi-

experimental)experimental)– Consists of a long series of observations during Consists of a long series of observations during

which a treatment is alternately administered which a treatment is alternately administered and then withdrawnand then withdrawnOOOXOOONOOOXOOONOOOXOOON…OOOXOOONOOOXOOONOOOXOOON…N – no treatmentN – no treatment

– It reduces likelihood of an external event It reduces likelihood of an external event confound to the treatmentconfound to the treatment

– Differences between expected temporary and Differences between expected temporary and permanent effectspermanent effects

4. Developmental research designs4. Developmental research designs the purpose is to describe the relationship between the purpose is to describe the relationship between

age and other variablesage and other variables Cross-sectional research design (nonexperimental)Cross-sectional research design (nonexperimental)

– uses different groups of individuals, each group uses different groups of individuals, each group representing a different agerepresenting a different age

– the different groups are measured at one point in time the different groups are measured at one point in time and then compared (e.g. IQ in 30, 40, 50 and 60 years and then compared (e.g. IQ in 30, 40, 50 and 60 years old)old)

– individuals who were born at roughly the same time and individuals who were born at roughly the same time and grew up under similar circumstances are called cohortsgrew up under similar circumstances are called cohorts

– the terms cohort effect or generation effect refer to a the terms cohort effect or generation effect refer to a difference between age groups (or cohorts) due to difference between age groups (or cohorts) due to unique characteristics or experiences other than age; unique characteristics or experiences other than age; generation effects are a type of third-variable problemgeneration effects are a type of third-variable problem

4. Developmental research designs4. Developmental research designs

Longitudinal research design (nonexperimental)Longitudinal research design (nonexperimental)– examines development by making a series of examines development by making a series of

observations or measurements over timeobservations or measurements over time– commonly the same group of individuals is followed and commonly the same group of individuals is followed and

measured at different points in timemeasured at different points in time– Avoids problems with cohort effects but is usually very Avoids problems with cohort effects but is usually very

time-consuming and expensivetime-consuming and expensive– Serious problem with participant attritionSerious problem with participant attrition– e.g. follow-up on IQ changes in the same group of e.g. follow-up on IQ changes in the same group of

subjects when they are 20 years old, 30, 40 and 50 subjects when they are 20 years old, 30, 40 and 50 years oldyears old