Updates to exact statistics were introduced in Stata 10.
Stata 10 offers several commands for exact analysis, providing more reliable statistical inference with small-sample datasets.
|bitest||Binomial probability test|
|cc||Case–control study odds ratios|
|ci||Centiles with confidence intervals|
|cs||Cohort study risk differences and ratios|
|ir||incidence-rate ratios and differences|
|ksmirnov||Two-sample Kolmogorov–Smirnov test|
|loneway||Large one-way analysis of variance|
|mcc||Matched case–control study statistics|
|symmetry||Symmetry and marginal homogeneity tests|
|tabulate2, tab2||Two-way tables with Fisher’s exact test|
Stata’s new exact logistic regression command provides better coverage in small samples than does standard logistic regression.
It also provides parameter estimates and confidence intervals where standard asymptotic methods cannot.
Such cases include small-data problems with binary regressors for which the outcome is 1 whenever the regressor is 1.
In the example below, every treated patient exhibits a positive response. Standard logistic regression cannot estimate the treatment effect. Stata 10’s new exlogistic command can:
. exlogistic response treatment x2 x3
Parameter estimates, standard errors, and CIs are calculated on the basis of permutation without recourse to asymptotic assumptions and results.
Not only is the treatment effect estimated, but tests of significance and reported confidence intervals are based on exact methods.
Stata 10 also includes exact Poisson regression for count data.