Lab Statistics from Study Counts
With Chi Square, NNT & "Cost to Treat" Estimates
Demonstration Only-Not for Official Use]
Chi-Square Statistics and Confidence Intervals
The Chi-Square section above estimates various additional statistics
from a 2-by-2 table. It estimates a Yates-corrected chi-square, along with confidence
intervals for other quantities relevant to two special kinds of 2-by-2 tables:
analysis of risk factors for unfavorable outcomes (odds
ratio, relative risk)
analysis of the effectiveness of a diagnostic criterion
for some conditions (sensitivity, specificity, positive predictive value,
negative predictive value)
These concepts are explained in detail in an online
Evidence-based Medicine Glossary.
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).
Relative Risk: If 2x2 data is from a cohort study (prospective),
then use the Relative Risk value which is the ratio of the rate of events in
the control (unexposed) group "a/a+b" to the rate of events in the experimental
(exposed) group "c/c+d".
Odds Ratio: If 2x2 data is from a case-control study, then use the Odds Ratio
value which is the ratio of the odds of disease for the experimental group
over the odds of disease for the control group. Or the ratio of the odds
of being exposed or unexposed in the "case" group "a/c" to the odds of
being exposed or unexposed the "control" group "b/d".
Copyright (c) Health Decision Strategies, LLC
Model developed from the R. Hamm Calculators and Roberto
Bissoni's Xpert program.
[For Demonstration Only - Beta Testing - Not for Official Use]