Statistical Power calculations for z-test for two independent samples.
currently only uses pooled variance
|plot_power([dep_var, nobs, effect_size, ...])||plot power with number of observations or effect size on x-axis|
|power(effect_size, nobs1, alpha[, ratio, ...])||Calculate the power of a t-test for two independent sample|
|solve_power([effect_size, nobs1, alpha, ...])||solve for any one parameter of the power of a two sample z-test|