How to get Effect Size from tt_ind_solve_power?

Question

I am trying to get the Effect Size given my alpha, power, sample size, ratio. I found tt_ind_solve_power to do this but how would this work for 4 variants + 1 control?

This is how I have it currently

from statsmodels.stats.power import tt_ind_solve_power

effect_size = tt_ind_solve_power(nobs1=X,
                                 alpha=0.05, 
                                 power=0.8, 
                                 ratio=1, 
                                 alternative='two-sided')

My goal is to get the effect size for my experiment with 4 variants. How do I define my nobs=X parameter in the function above? And would the outcome be the effect size per variant or in aggregate?

Sample Sizes:
    Variant 1: 990
    Variant 2: 1001
    Variant 3: 1100
    Variant 4: 999
    Control:  1002

Any help is very much appreciated!

Asked By: titutubs

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Answer 1

If I understand the question correctly, we need sample size for the treatment, nobs1, and ratio for the power effectsize computation.

ratio is defined by nobs2 = nobs1 * ratio, so ratio = nobs2 / nobs1 where nobs2 is the number of observations of the control or reference treatment.

For comparing variant1 with the control use:

nobs1 = 990
ratio = 1002 / nobs1

and similar for nobs1 of the other variants or treatments.

Answered By: Josef

How to get Effect Size from tt_ind_solve_power?

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