Biostatistics Flashcards
Case control study
a. Compares what?
b. Looks for what?
c. Measured by?
d. Asks what?
e. Retrospective or Prospective?
a. Compares a group of people WITH disease to group of people WITHOUT disease
b. Looks for prior exposure or risk factor
c. Measured by odds ratio
d. Asks “what happened?”
e. Retrospective and observational
Cohort study
a. Compares what?
b. Looks for what?
c. Measured by?
d. Asks what?
e. Retrospective or Prospective?
a. Compares a group of people with a given exposure or risk factor to a group without such exposure.
b. Looks to see if exposure increases the likelihood of disease
c. Measured by relative risk
d. Asks either “Who will develop disease?” or “Who developed the disease?”
e. Can be retrospective or prospective
What is odds ratio?
Odds that the group with the disease (case) was exposed to a risk factor divided by the odds that the group without the disease (controls) was exposed; odds ratio
What is relative risk?
Risk of developing disease in the exposed group divided by risk in the unexposed group; relative risk
Cross-sectional study
a. Design?
b. Asks what?
c. Measures what?
a. Collects data from a group of people to assess frequency of disease (or risk factor) at a particular point in time.
b. What is happening?
c. Disease prevalence
Twin concordance study
a. Design?
a. Compares the frequency with which both monozygotic twins and both dizygotic twins develop the same disease
Adoption study
a. Design?
a. Compares siblings raised by biological vs. adoptive parents
Phase I Clinical Trial
a. Typical study sample
b. Purpose
a. Small number of healthy volunteers (medical students)
b. “Is it safe?” Assesses safety, toxicity, pharmacokinetics, pharmacodynamics
Phase II Clinical Trial
a. Typical study sample
b. Purpose
a. Small number of patients with disease of interest
b. “Does it work?” Assesses treatment efficacy, optimal dosing, adverse effects
Phase III Clinical Trial
a. Typical study sample
b. Purpose
a. Large number of patients randomly assigned either to treatment under investigation or best available treatment
b. “Is it as good or better?” Compares new treatment to the current standard of care
Phase IV Clinical Trial
a. Typical study sample
b. Purpose
a. Postmarketing surveillance of patients after treatment is approved
b. “Can it stay?” Detects rare or long-term adverse effects. Can result in treatment being withdrawn from market
Sensitivity equation
True positives/True positives + False negatives OR
1 - false negative rate
Specificity equation
True negatives/True negatives + False positives OR
1 - false positive rate
PPV equation
True positives/ True positives + False positives
NPV equation
True negatives/ True negatives + False negatives
Odds ratio equation
(A/B)/(C/D)
Relative risk equation
A/(A+B) / C/(C+D)
Attributable risk
A/(A+B) - C/(C+D)
Absolute risk reduction
C/(C+D) - A/(A+B)
Relative risk reduction
1 - RR
Number Needed to Treat
1/ARR
Number Needed to Harm
1/AR
What is precision?
Consistency and reproducibility of a test (reliability)
What is accuracy?
Trueness of test measurements (validity)
What is selection bias?
Error in assigning subjects to a study group resulting in an unrepresentative sample; most common a sampling bias
Berkson bias?
Study population selected from hospital is less healthy than general population
Recall bias?
Awareness of disorder alters recall by subjects, common in retrospective studies
Sampling bias?
Study population does not accurately represent the target population
Late-look bias?
Results from info being gathered too late to accurately sample entire population
Procedure bias?
Subjects in different groups are not treated the same
Lead-time bias?
Early detection is confused with increased survival
Observer-expectancy bias? (Pygmalion effect)
Researcher’s beliefs in the efficacy of a treatment changes the outcome of that treatment - self-fulfilling prophecy
Confounding bias?
When a factor is related to both the exposure and outcome but not on the causal pathway –> factor distorts or confuses effect of exposure on outcome
-Pulmonary disease is more common in coal workers than general population BUT people who work in coal mines also smoke more frequently than the general population
