biostats

Question 1

What kind of stats come from a case control study?

Answer 1

odds ratio: “ patients with COPD had a higher odds of a history of smoking than those without COPD had”

Question 2

what kind of stats come from a cohort study

Answer 2

relative risk. compares a group with a given exposure to a group without such an exposure. “smokers had a higher risk of developing COPD than non-smokers.”

Question 3

What questions are asked at each phase of a clinical trial?

Answer 3

phase I: is it safe?
phase II: Does it work? (efficacy, dosing, adverse effects)
phase III: Is it as good or better than other treatments?
phase IV: postmarketing surveillence of pts after approval- looks lfor rare/long-term effects of the drug

Question 4

when is high sensitivity the most important?

Answer 4

when you are “ruling out” a condition.

also needed when screening a disease with low prevalence

Question 5

odds ratio

Answer 5

used in case-control studies
odds that the group with the disease was exposed to a risk factor divided by the odds that the group without the disease was exposed. (a/c)/(b/d)

Question 6

relative risk

Answer 6

used in cohort studies. risk of developing the disease in the exposed group divided by the risk in the unexposed group. (a/(a+b))/(c/(c+d))

Question 7

relative risk reduction

Answer 7

proportion of risk reduction attributable to the intervention: RRR = 1-RR. (if 2% of pts who receive a flu shot develop flu vs. 8% of unvaccinated, RR = 2/8 = .25. RRR = .75)

Question 8

attributable risk

Answer 8

difference in risk btw exposed and unexposed groups, or the proportion of disease occurrences that are attributable to the exposure. (a/(a+b))-(c/(c+d))

Question 9

absolute risk

Answer 9

difference in risk attributable to the intervetion as compared to a control. (8% of ppl who receive a placebo get flu vs 2% who receive a flu shot, then 8%-2%= 0.06

Question 10

number needed to treat

Answer 10

1/absolute risk reduction

Question 11

number needed to harm

Answer 11

number of pts who need to be exposed to a risk factor for 1 pt to be harmed. 1/absolute risk

Question 12

Hawthorne effect

Answer 12

groups who know they’re being studied behave differently than they would otherwise

Question 13

How are crossover studies useful?

Answer 13

can reduce confounding bias. subjects act as their own controls (they switch from exposure to non-exposure), but obviously keep the confounding variables the same
matching can also reduce confounding

Question 14

How do you address lead time bias?

Answer 14

measure back end survival- adjust survival according to the severity of disease at diagnosis