Epidemiology &
Lab Statistics from Study Counts
With Chi Square, NNT & "Cost to Treat" Estimates
[For
Demonstration OnlyNot for Official Use]
ChiSquare Statistics and Confidence Intervals
The ChiSquare section above estimates various additional statistics
from a 2by2 table. It estimates a Yatescorrected chisquare, along with confidence
intervals for other quantities relevant to two special kinds of 2by2 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
Evidencebased Medicine Glossary.
Confidence intervals for the estimated parameters are computed by a general method given in:
Statistical Methods for Rates and Proportions (2^{nd} 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 casecontrol 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]
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