statsmodels.stats.power.TTestPower.solve_power

TTestPower.solve_power(effect_size=None, nobs=None, alpha=None, power=None, alternative='twosided')
[source]

solve for any one parameter of the power of a one sample ttest
 for the one sample ttest the keywords are:
 effect_size, nobs, alpha, power
Exactly one needs to be None
, all others need numeric values.
This test can also be used for a paired ttest, where effect size is defined in terms of the mean difference, and nobs is the number of pairs.
Parameters: 

effect_size (float) – standardized effect size, mean divided by the standard deviation. effect size has to be positive.

nobs (int or float) – sample size, number of observations.

alpha (float 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.

power (float in interval (0,1)) – power of the test, e.g. 0.8, is one minus the probability of a type II error. Power is the probability that the test correctly rejects the Null Hypothesis if the Alternative Hypothesis is true.

alternative (string, 'twosided' (default) or 'onesided') – extra argument to choose whether the power is calculated for a twosided (default) or one sided test. ‘onesided’ assumes we are in the relevant tail.

Returns: 

value (float) – The value of the parameter that was set to None in the call. The value solves the power equation given the remaining parameters.
 *attaches*

cache_fit_res (list) – Cache of the result of the root finding procedure for the latest call to
solve_power , mainly for debugging purposes. The first element is the success indicator, one if successful. The remaining elements contain the return information of the up to three solvers that have been tried. 
Notes
The function uses scipy.optimize for finding the value that satisfies the power equation. It first uses brentq
with a prior search for bounds. If this fails to find a root, fsolve
is used. If fsolve
also fails, then, for alpha
, power
and effect_size
, brentq
with fixed bounds is used. However, there can still be cases where this fails.