pingouin.pairwise_gameshowell

pingouin.
pairwise_gameshowell
(data=None, dv=None, between=None, alpha=0.05, tail='twosided', effsize='hedges')[source] Pairwise GamesHowell posthoc test.
 Parameters
 datapandas DataFrame
DataFrame
 dvstring
Name of column containing the dependant variable.
 between: string
Name of column containing the between factor.
 alphafloat
Significance level
 tailstring
Indicates whether to return the ‘twosided’ or ‘onesided’ pvalues
 effsizestring or None
Effect size type. Available methods are
'none' : no effect size 'cohen' : Unbiased Cohen d 'hedges' : Hedges g 'glass': Glass delta 'etasquare' : Etasquare 'oddsratio' : Odds ratio 'AUC' : Area Under the Curve
 Returns
 statsDataFrame
Stats summary
'A' : Name of first measurement 'B' : Name of second measurement 'mean(A)' : Mean of first measurement 'mean(B)' : Mean of second measurement 'diff' : Mean difference (= mean(A)  mean(B)) 'se' : Standard error 'tail' : indicate whether the pvalues are onesided or twosided 'T' : Tvalues 'df' : adjusted degrees of freedom 'pval' : GamesHowell corrected pvalues 'hedges' : effect size (or any effect size defined in ``effsize``)
Notes
GamesHowell is very similar to the Tukey HSD posthoc test but is much more robust to heterogeneity of variances. While the TukeyHSD posthoc is optimal after a classic oneway ANOVA, the GamesHowell is optimal after a Welch ANOVA. GamesHowell is not valid for repeated measures ANOVA.
Compared to the TukeyHSD test, the GamesHowell test uses different pooled variances for each pair of variables instead of the same pooled variance.
The Tvalues are defined as:
\[t = \frac{\overline{x}_i  \overline{x}_j} {\sqrt{(\frac{s_i^2}{n_i} + \frac{s_j^2}{n_j})}}\]and the corrected degrees of freedom are:
\[v = \frac{(\frac{s_i^2}{n_i} + \frac{s_j^2}{n_j})^2} {\frac{(\frac{s_i^2}{n_i})^2}{n_i1} + \frac{(\frac{s_j^2}{n_j})^2}{n_j1}}\]where \(\overline{x}_i\), \(s_i^2\), and \(n_i\) are the mean, variance and sample size of the first group and \(\overline{x}_j\), \(s_j^2\), and \(n_j\) the mean, variance and sample size of the second group.
The pvalues are then approximated using the Studentized range distribution \(Q(\sqrt2*t_i, r, v_i)\).
Note that the pvalues might be slightly different than those obtained using R or Matlab since the studentized range approximation is done using the Gleason (1999) algorithm, which is more efficient and accurate than the algorithms used in Matlab or R.
References
 1
Games, Paul A., and John F. Howell. “Pairwise multiple comparison procedures with unequal n’s and/or variances: a Monte Carlo study.” Journal of Educational Statistics 1.2 (1976): 113125.
 2
Gleason, John R. “An accurate, noniterative approximation for studentized range quantiles.” Computational statistics & data analysis 31.2 (1999): 147158.
Examples
Pairwise GamesHowell posthocs on the pain threshold dataset.
>>> from pingouin import pairwise_gameshowell, read_dataset >>> df = read_dataset('anova') >>> pairwise_gameshowell(data=df, dv='Pain threshold', ... between='Hair color')