statsmodels.stats.rates.power_poisson_diff_2indep

statsmodels.stats.rates.power_poisson_diff_2indep(rate1, rate2, nobs1, nobs_ratio=1, alpha=0.05, value=0, method_var='score', alternative='two-sided', return_results=True)

Power of ztest for the difference between two independent poisson rates

Parameters:

rate1float

Poisson rate for the first sample, treatment group, under the alternative hypothesis.

rate2float

Poisson rate for the second sample, reference group, under the alternative hypothesis.

nobs1float or int

Number of observations in sample 1.

nobs_ratiofloat

Sample size ratio, nobs2 = nobs_ratio * nobs1.

alphafloat in interval (0,1)

Significance level, e.g., 0.05, is the probability of a type I error, that is wrong rejections if the Null Hypothesis is true.

valuefloat

Difference between rates 1 and 2 under the null hypothesis.

method_var{“score”, “alt”}

The variance of the test statistic for the null hypothesis given the rates under the alternative, can be either equal to the rates under the alternative method_var="alt", or estimated under the constrained of the null hypothesis, method_var="score".

alternative{‘two-sided’, ‘larger’, ‘smaller’}

Alternative hypothesis whether the power is calculated for a two-sided (default) or one sided test. The one-sided test can be either ‘larger’, ‘smaller’.

return_resultsbool

If true, then a results instance with extra information is returned, otherwise only the computed power is returned.

Returns:

PowerDiffResult or float

If return_results is False, then only the power is returned as a float. If return_results is True (default), then a PowerDiffResult result object is returned; it behaves like the scalar power in numeric comparisons (e.g., assert_allclose), while also exposing std_null, std_alt and other attributes.

References

[1]

Stucke, Kathrin, and Meinhard Kieser. 2013. “Sample Size Calculations for Noninferiority Trials with Poisson Distributed Count Data.” Biometrical Journal 55 (2): 203-16. https://doi.org/10.1002/bimj.201200142.

[2]

PASS manual chapter 436