Study Design Flashcards
What is selection bias?
Error in the sampling of individuals for a clinical study. Ex: Subjects chosen for the case and control group differ
What is observational bias?
Error in the recording of the factors of the study. Ex: inaccurate recording of a patient’s risk factor
What is recall bias?
Systematic error caused by differences in the accuracy or completeness of recollections of study participants regarding past events or experiences
What is interviewer bias?
Ex: interviews are not conducted in a uniform manner for all participants
What are the disadvantages of case reports/series?
Does not provide explanation other than conjecture and does not establish causality of association
What are the advantages of case reports/series?
Hypothesis can be formed. Easy to perform and are inexpensive
Case-Control study
Study exposure in those with and without outcomes of interest
What kind of studies are retrospective studies?
Observational
What category of study should be chosen to study exposures in rare diseases that take long periods to develop?
Observational
What assumptions must be made to minimize bias in observational studies?
-Cases are selected to be representative of those who have the disease
-Controls are representative of general population
-Information is collected from case and controls in the same way
What kind of bias are case-control studies most vulnerable to?
-Observational and recall bias
-Selection bias
What is the most common measure of association used for case-control studies?
OR or RR
Can RR be calculated from prospective or case-control studies?
Prospective
If RR <1 what can be the interpretation?
Risk of disease is lower in the exposed group
If RR =1 what can be the interpretation?
No association
If RR/OR >1 what is the association?
Positive association
Calculate the OR. A total of 7 women are exposed to PPA. 1126 of women included in the study were not exposed to PPA. Out of the women who were not exposed to PPA, 377 experienced hemorrhagic stroke. Out of the women who were exposed to PPA women experienced hemorrhagic stroke.
OR = (6/377)/(1/749)=12
What is the most common situation in which non inferiority trials are used?
When placebo administration is not possible for ethical reasons
Do intention-to-treat vs per-protocol analysis have more information about treatment efficacy?
Per-protocol
Do intention-to-treat or per-protocol analysis have greater external validity?
Intention-to treat
What is the difference between systemic reviews and meta-analysis?
Systemic reviews perform comprehensive lit search and synthesize literature on a topic. Meta-analysis use mathematical/statistical techniques to summarize the results of evaluated studies
What is the calculation for NNT?
NNT=1/ARR *generally round to the next highest whole number
ARR= (experimental event rate)-(control event rate)
What must apply to a study in order to properly calculate a NNT?
-Outcomes must be dichotomous (yes/no, alive/dead)
-Outcomes must be statistically significant
What is the difference between a cost-effectiveness analysis and cost-utility analysis?
Cost-utility analysis assigned utility weights to outcomes (Ex: quality-adjusted life-years) and cost-effectiveness analysis assigned cost per unit health outcome(ex:number of symptom free days)
