lecture 4, research design (slides)
TRANSCRIPT
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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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Choosing a research questions
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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Choosing a research questions
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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Choosing a research questions
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