Cross-sectional study measures....

Disease prevalence

Case-control study measures...

Odds ratio (OR)

Cohort study measures....

Relative risk (RR)

Prevalence of diseases with short duration =

roughly the incidence rate

OR =

(A/C) / (B/D)

RR =

[a/(a+b)] / [c/(c+d)]

AR =

a/a+b - c/c+d

RRR =

1 - RR

ARR -

c/c+d - a/a+b

NNT =

1/ARR

NNH =

1/AR

Attributable risk % in the exposed =

100 x (RR-1)/RR

Increased precision...

Increased statistical power

berkson bias

study pop selected from hospital is less healthy than general pop

Pygmalion effect

Researchers belief in efficacy of Tx changes the outcome

Hawthorne effect

subjects change behavior when they know they are being observed (observer effect)

SEM (standard error of the mean) =

SD/square root of n (SEM decreases w/ increased sample size

Increased power by:

increasing sample size, expected effect size, precision of measurement

For the 95% CI, Z = For the 99% CI, Z =

1.96 2.58

CI =

mean +/- Z x SEM

Sensitivity =

1 - false negative rate

Specificity =

1 - false positive rate

Errrors

Coeffecient of determination

R^{2}

Medicare

Patients above 64

Under 65 with certain disabilites

Those with end-stage renal disease

Medicaid

Joint federal and state program for people with very low income

Medicare parts

A - hospital insurAnce

B - Basic medical Bils

C - (Parts A+B) delivered by approved private Companies

D - Prescription Drugs