lecture 4, research design (slides)

8/3/2019 lecture 4, Research Design (slides)

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Designing a study I

Research Methods

Dent 313


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Choosing a research question First step of research design

Identifying a research question

Determine the unknowns in your field

What do you wish you knew in your field? What does the available literature lack? Your capacity and experience

Research question Descriptive Analytic


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Descriptive research question Explaining clinical phenomena

Prevalence of disease E.g. (Prevalence of caries among school children)

Survival trends E.g. (% of men w prostate cancer alive at 5 years)

Health service utilization E.g. (% seniors receiving H1N1 vaccination)

Clinical test characteristics E.g. (mean value of LDL among patients w IHD)


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Analytic research question

Comparative

E.g. (Is prevalence of caries higher among private orgovernmental school children?)

More significant than descriptive questions Answering enable to

develop intervention to prevent disease Target intervention to particular population

Descriptive questions must be answered first


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Choosing a research questions

Specify the population

Determine the length of the study and your

willingness towards completion Median time from enrolling subjects to

publication was found to be 5.5 (J.P. Ioanndis)


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1st criterion

Choose a question that keeps youexcited all the way through

Identify obstacles to performing andpublishing research Subjects, ethical approval, collaborators, lab

capacity, review committees, editors, missing data


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Choosing a research question

2nd criterion

Choose a question that will have animpact on the health and well being ofthe population

Difficult to fully appreciate the impact a studywill have before doing it Modifications, groundbreaking results,

discoveriesetc

Purpose of clinical research is to improvehealth not for grantsmanship, publication andpromotion

Enrollment of sufficient number of subjects


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3rd criterion

Consider what questions you are readyto answer based on

The prevalence of the disease in your area Your prior experience Your colleagues Your community contacts


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4th criterion

Be sure it has not already beenanswered unless if you can do better

Computerized literature searches Consulting the others in the field Attending conferences

Scientific / academic relations

Not all conference abstracts are electronicallyaccessible


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Choosing a study design

There is no best study design

Determine the best study design to

answer your question Feasibility, cost, length of time, risks and

benefits on participants

Broad categories of study design Randomized studies Observational studies


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Differences between randomized and

observational studies

Randomized Investigator manipulates the condition or

group assignment

One group receives a treatment Another receives a different treatment or placebo

Observational Investigator assesses a population without

altering the condition or group assignment ofthe population


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Advantages & disadvantages of

randomized studies

Better at dealing with confounding andbias

Less generalizability Slower to conduct

More expensive

Cannot answer as broad a range ofquestions as observational studies


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Confounding

Association between a risk factor and anoutcome is affected by the relationship of

a third variable (confounder) to the riskfactor or the outcome

Confounder

Associated with the risk factor

Causally related to the outcome


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Confounding

Risk factor

Confounder

Outcome

Randomized groupassignment

Potentialconfounder

Outcome

With randomization there should be no relationship confounder and group assignment


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Eliminating confounding

Randomizing subjects

Randomization should be unbiased

Randomized groups will be equal with respectto confounders

Randomization eliminates known and unknownconfounders

Other techniques for minimizing knownconfounders Matching, stratification, multivariable adjustment


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Minimizing bias

Randomization eliminates confoundingonly when unbiased

Group assignment should be done at the time of enrollment not before or after

No group assignment change by personnel by someone with no contact with the subject using a random number table or generator


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Minimizing bias

In observational studies, investigatorsand subjects usually know which group

the subject / examiner were assigned to Investigators may have some expectation onwhat the outcome would be (possibility ofbias)

Subject may leave the study if they know theybelong to control (not treatment) group


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Minimizing bias

Blinding in randomized trial

Preventing both the investigator and thesubject from knowing group assignment

Double blinded vs. single blinded Double blinding is impossible with

observational studies


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Generalizability

Generalizability refers to the ability toapply the outcomes of a study to

populations other than the study sample The results of a trial apply only to

populations that resemble the studysample


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Generalizability and randomized

studies

Generalizability is more a problem with randomizedstudies

Randomized subjects are different from the generalpopulation because they carry more burdens Selection, blinding, previous exams and blood testsetc.

Trial conditions are different from those in clinical practice Trial subjects receive more attention

Treatment works under tight research protocol Treatment efficacy vs. treatment effectiveness Efficacy: how well an intervention works in a research setting Effectiveness: how well an intervention works in a clinical setting


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Observational studies and

treatment effectiveness

Closer together than in randomizedstudies

Still some differences Observational study patients receive

additional educational or testing than normalclinical patients

Observational study patients may changetheir behavior (Hawthrone effect)


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Length of time to conduct

Observational studies are faster toconduct than randomized studies

Especially with an existing database and theuse of case-control design


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Minimizing expenses

Observational studies are less expensive Especially with an existing database and the use of

case-control design

Less markedly with prospectivecohort design Observers are just observing the outcomes

Randomized control trials are expensive

Paying for all of the interventions e.g. medicines, tests, appliances..etc.


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Addressing a broader range of

questions

Observational studies are able to answera broader range of questions

Many situations where it is unethical orimpractical to randomize subjects (you cannotrandomize persons to smoke or not to smoke)

Randomized control studies are rarely helpful

in identifying causes of disease outbreaks


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Indications of observational

studies

Instances where it is unethical orimpractical to perform a randomized

study Time is of the essence in obtaining the

results

lecture 4, research design (slides)

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