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30 Cards in this Set

  • Front
  • Back
1. Case-control study?
a. Observational and retrospective
b. Compares a group of people w/a disease to a group w/out.
c. Asks, “What happened”?
d. Measures: Odds Ratio (OR)
i. “Patients w/COPD had higher odds of a hx of smoking than those w/out COPD”.
2. Cohort study?
a. Observational and prospective
b. Compares a group w/a given risk factor to a group w/out to assess whether the risk factor increased the likelihood of disease.
c. Asks “What will happen?”
d. Measures Relative risk (RR).
i. “Smokers had a higher risk of developing COPD than did non-smokers.
3. Cross-sectional study?
a. Observational
b. Collects data from a group of people to assess frequency of disease (and related risk factors) at a particular point in time.
c. Asks, “what is happening?”
d. Measures: Disease Prevalence.
i. Can show risk factor association w/disease, but does not establish causality.
4. Twin Concordance study?
a. Compares the frequency with which monozygotic twins or both dizygotic twins develop a disease.
b. Measures heritability.
5. Adoption study?
a. Compares siblings raised by biologic vs. adoptive parents.
b. Measures heritability and influence of environmental factors
6. Highest quality clinical trial?
a. Randomized, controlled, and double-blinded.
7. Phase I clinical trial?
a. Small number of pts, usually healthy volunteers.
b. Purpose: Assesses safety, toxicity, and pharmacokinetics.
8. Phase II clinical trial?
a. Small number of pts w/disease of interest.
b. Assesses treatment efficacy, optimal dosing, and adverse effects.
9. Phase III Clinical trial?
a. Large number of pts randomly assigned either to the treatment under investigation or to the best available treatment (or placebo).
b. Compares the new treatment to the current standard of care.
c. Is more convincing if double blinded (i.e. neither patient nor doctor knows if the patient is in the treatment or control group).
10. Meta-analysis?
a. Pools data from several studies to come to an overall conclusion.
b. Achieves greater statistical power and integrates results of similar studies.
c. Highest echelon of clinical evidence.
d. May be limited by quality of individual studies or bias in study selection.
11. Prevalence vs. Incidence?
a. Prevalence= total cases in population at a given time/total population at risk.
i. Prevalence ~ incidence x disease duration.
b. Incidence= time period/Total population at risk during that time.
i. Incidence is new incidents.
12. Prevalence > incidence for?
a. Chronic diseases (e.g. DM)
13. Prevalence = incidence for?
a. Acute disease (e.g. common cold)
14. Note: when calculating incidence, don’t forget that people previously positive for disease are not longer considered at risk.
14. Note: when calculating incidence, don’t forget that people previously positive for disease are not longer considered at risk.
15. Disease sensitivity specificity box?
a. Disease

+ -
+ A B
- C D
16. Sensitivity?
a. Proportion of all people w/disease who test positive.
b. =a/ (a+c)
c. Value approaching 1 is desirable for ruling OUT disease and indicates a low false-negative rate.
d. Used for screening in disease w/low prevalence.
17. Specificity?
a. Proportion of all people w/out disease who test negative.
b. Value approaching 1 is desirable for ruling in disease and indicates a low false-positive rate.
c. Used as a confirmatory test after a positive screening test.
d. = d/ (d+b).
e. =1-false-positive rate.
18. Specificity example?
a. HIV testing. Screen w/ELISA (sensitive, high false-positive rate, low threshold). Confirm w/western blot (specific, high false-negative rate, high threshold).
19. Sensitivity mnemonic?
a. SNOUT= SeNsitivity rules OUT.
20. Specificity mnemonic?
a. SPIN= Specificity rules IN.
b. E.g.
21. Positive predictive value (PPV)?
a. Proportion of positive test results that are true positive.
b. =a / (a+b)
c. Probability that person actually had the disease given a positive test result.
d. Note: If the prevalence of a disease in a population is low, even tests w/high specificity or high sensitivity will have low positive predictive values.
22. Negative predictive value (NPV)?
a. Proportion of negative test results that are true negative. = d (c+d).
b. Probability that person actually is disease free given a negative test result.
23. Odds ratio (OR) for case control studies?
a. Odds of having disease in exposed group divided by odds of having disease in unexposed group.
b. Approximates relative risk if prevalence of disease is not too high.
24. Odds ratio formula?
a. Odds ratio = (a/b)/(c/d) = (ad)/(bc)
25. Relative risk (RR) for cohort studies?
a. Relative probability of getting a disease in the exposed group compared to the unexposed group.
b. Calculated as percent w/disease in exposed group divided by percent w/disease in unexposed group.
26. Relative risk formula?
a. [a/(a+b)]/[c/(c+d)].
27. Attributable risk?
a. The difference in risk between exposed and unexposed groups, or the proportion of disease occurrences that are a result of the exposure (e.g., smoking causes 1/3 of cases of pneumonia.
28. Attributable risk formula?
a. Attributable risk= [a/(a+b)] - [c/(c+d)].
29. Precision vs. accuracy?
a. Precision is:
1. The consistency and reproducibility of a test (reliability)
2. The absence of random variation in a test.
b. Accuracy is The trueness of test measurements (validity).
30. Random error and systematic error w/respect to precision and accuracy?
a. Random error = reduced precision in a test.
b. Systematic error = reduced accuracy in a test.