title: Calculate `eta` for sample size calculation using power anova
body: <p>I am using <code>pingouin.power_anova(eta=None, k=None, n=None, power=None, alpha=0.05)</code> in python for the calculation of sample size.
  I have the information about <code>control_group_historic_mean</code>, <code>control_group_historic_std_deviation</code> and <code>minimum_detectable_effect</code>. I read about the definition of <code>eta</code> from <a href="https://www.easycalculation.com/statistics/eta-square-calculator.php" rel="nofollow noreferrer">here</a>. But not able to figure out how should i use the given information to calculate <code>eta</code>.</p>
  <p>Sorry if I am missing something basic, I am new to statistics.</p>