Cross-sectional study

observational. Collects data from a group of people to assess frequency of disease ( and related risk factors)

Case-control study

Observational and retrospective. Compares a group of people with disease to a group without disease. Odds ratio

Cohort study

Observational and prospective or retrospective. Compares a group with a given exposure or risk factor to a group without such exposure. Relative risk

Diagnostic test evaluation

Odds ratio

(a/c)/(b/d) Case-control studies

Relative risk

(a/(a+b))/(c/(c+d)) cohort studies

Relative risk reduction

1 - RR

Attributable risk

AR = a/(a+b) - c/(c+d)

Absolute risk reduction

the difference in risk (not the proportion) attributable to the intervention as compared to a control (e.g. if 8% of people who receive a placebo vaccine develop flu vs 2% of people who receive a flu vaccine, then ARR= 8%-2%=6%

Number needed to treat

1/ARR

Number needed to harm

1/AR

Berkson bias

A study only looking at inpatients

Hawthorne effect

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

Pygmalion effect

(self-fulfilling prophecy) - Researcher's belief in the efficacy of a treatment changes the outcome of that treatment

Statistal hypotheses

Power

1-B - Probability of rejecting the null hypotheses when it is false. increase power and decrease B by increasing sample size, increase expected effect size, and increasing precision of measurment

Confidence Interval

CI=range from [mean-Z(SEM)] to [mean+Z(SEM)] for 95% CI Z=1.96, 99% Z =2.58

SEM = sigma/sqrt(n) sigma=stdDev