2-way Contingency Table Analysis

This page computes various statistics from a 2-by-2 table. It will calculate a Yates-corrected chi-square, along with other quantities relevant to two special kinds of 2-by-2 tables:

  1. analysis of risk factors for unfavorable outcomes (odds ratio, relative risk, difference in proportions, number needed to treat)
  2. analysis of the effectiveness of a diagnostic criterion for some conditions (sensitivity, specificity, positive predictive value, negative predictive value)

Confidence intervals for the estimated parameters are computed by a general method given in: Statistical Methods for Rates and Proportions (2nd Ed.) by Joseph L. Fleiss (Pub: John Wiley & Sons, New York, 1981)

Enter numbers into the four cells below. Make sure that the row and column totals add up correctly. Then click the Compute button.

*
Outcome Occurred
Outcome did not Occur
Totals
Risk Factor Present
or Dx Test Positive
Risk Factor Absent
or Dx Test Negative
Totals




Chi Square
d.f.
p


Quantities Derived From A 2-by-2 Table
Statistic
Value
Low 95% CI
Hi 95% CI
Odds Ratio
Relative Risk
Kappa
Sensitivity
Specificity
Pos Pred Val
Neg Pred Val
Diff in Proportions
# Needed to Treat