statsmodels.stats.weightstats.zconfint(x1, x2=None, value=0, alpha=0.05, alternative='two-sided', usevar='pooled', ddof=1.0)[source]

confidence interval based on normal distribution z-test

x1array_like, 1-D or 2-D

first of the two independent samples, see notes for 2-D case

x2array_like, 1-D or 2-D

second of the two independent samples, see notes for 2-D case


In the one sample case, value is the mean of x1 under the Null hypothesis. In the two sample case, value is the difference between mean of x1 and mean of x2 under the Null hypothesis. The test statistic is x1_mean - x2_mean - value.

usevarstr, ‘pooled’

Currently, only ‘pooled’ is implemented. If pooled, then the standard deviation of the samples is assumed to be the same. see CompareMeans.ztest_ind for different options.


Degrees of freedom use in the calculation of the variance of the mean estimate. In the case of comparing means this is one, however it can be adjusted for testing other statistics (proportion, correlation)

See also



checked only for 1 sample case

usevar not implemented, is always pooled in two sample case

value shifts the confidence interval so it is centered at x1_mean - x2_mean - value

Last update: Jul 16, 2024