Biostat Flashcards
Case-Control Study
Compare a group of people WITH disease to a group WITHOUT disease, looking for PRIOR exposure or risk factor. “What happened?”
Cohort Study
Compares a group WITH a given exposure or risk factor to a group WITHOUT such exposure, looking to see if an exposure INCREASED the likelihood of disease. “Who will develop disease?” or “Who developed the disease?”
Cross-sectional Study
Collects data from a group of people to assess the FREQUENCY of disease and related risk factors at a particular point in time. “What is happening?”
Phase I clinical trial
Small number of HEALTHY volunteers - assess safety, toxicity, and pharmacokinetics
Phase II clinical trial
Small number of patients WITH DISEASE OF INTEREST - assess treatment efficacy, optimal dosing, and adverse effects
Phase III clinical trial
LARGE number of patients randomly assigned either to the treatment under investigation or to the best available treatment or placebo - COMPARES the new treatment to current standards
Phase IV clinical trial
POSTMARKETING SURVEILLANCE trial of patients after approval - detects rare or long-term adverse effects
How does PPV vary with prevalence
It varies directly with prevalence or pretest probability i.e. high pretest probability –> high ppv
How does NPV vary with prevalence
It varies inversely with prevalence or pretest probability i.e. high pretest probability –> low NPV
Odds ratio
Odds that the group with the disease (CASES) was exposed to a risk factor divided by the odds that the group without the disease (CONTROLS) was exposed; used in case-control studies
Relative Risk
Risk of developing disease in the exposed group divided by risk in the unexposed group; used in cohort studies
RR = 1 indicates what?
That risk of developing disease is the same in exposed and unexposed individuals
Attributable Risk
Difference in risk between exposed and unexposed groups, or the proportion of disease occurrences that are attributable to the exposure
Absolute Risk Reduction
Absolute reduction in risk associated with a treatment as compared to a control
Number needed to treat
Number of patients who need to be treated for 1 patient to benefit. 1/absolute risk reduction
Number needed to harm
Number of patients who need to be exposed to a risk factor for 1 patient to be harmed. 1/attributable risk
Effect modification
The effect of the main exposure on the outcome is modified by the presence of another variable
Selection bias
Nonrandom assignment to participation in a study group
Recall bias
Knowledge of presence of disorder alters recall subjects; common in retrospective studies
Sampling bias
Subjects not representative of general population; type of selection bias
Late-look bias
Information gathered at an inappropriate time i.e. using a survey to study a fatal disease - only patients still alive can answer
Procedure bias
Subjects in different groups are not treated the same
Confounding bias
Occurs when factor is related to both exposure and outcome, but is not on the causal pathway
Lead-time bias
Early detection confuse with increased survival
