Pros and cons of study designs Flashcards
Pros of RCT
Unbiased distribution of confounders
Blinding more likely
Randomisation facilitates statistical analysis
Cons of RCT
Expensive: time and money
Volunteer bias
Ethically problematic at times
Pros of crossover
All participants serve as own controls and error variance is reduced, thus reducing sample size needed
All participants receive treatment (at least some of the time)
Statistical tests assuming randomisation can be used
blinding can be maintained
Cons of crossover
All participants receive placebo or alternative treatment at some point
Washout period lengthy or unknown
Cannot be used for treatments with permanent effects
Pros of cohort study
Ethically safe
Participants can be matched
Can establish timing and directionality of events
Eligibility criteria and outcome assessments can be standardised
Cons of cohort study
Controls may be difficult to identify
Exposure may be linked to a hidden confounder
Blinding is difficult
For rare disease, large sample sizes or long follow-up necessary
Pros of case control
Quick and cheap as fewer people needed than cross-sectional studies
Only feasible method for very rare disorders or those with long lag between exposure and outcome
Cons of case control
Reliance on recall or records to determine exposure status
Confounders
Selection of control groups is difficult
Potential bias: recall, selection
Pros of cross sectional study
Cheap and simple
Ethically safe
Cons of cross sectional study
Establishes association at most, not causality
Recall bias, social desirability bias
Researcher’s (Neyman) bias
Group sizes may be unequal
Confounders may be unequally distributed
Neyman bias is when a series of survivors is selected, if the exposure is related to prognostic factors, or the exposure itself is a prognostic determinant, the sample of cases offers a distorted frequency of the exposure
