correct_glass_bias {psychmeta}

Correct for small-sample bias in Glass' \Delta values

Description

Correct for small-sample bias in Glass' \Delta values.

Usage

correct_glass_bias(delta, nc, ne, use_pooled_sd = rep(FALSE, length(delta)))

Arguments

delta

Vector of Glass' \Delta values.

nc

Vector of control-group sample sizes.

ne

Vector of experimental-group sample sizes.

use_pooled_sd

Logical vector determining whether the pooled standard deviation was used (TRUE) or not (FALSE; default).

Details

The bias correction is estimated as:

\Delta_{c}=\Delta_{obs}\frac{\Gamma\left(\frac{n_{control}-1}{2}\right)}{\Gamma\left(\frac{n_{control}-1}{2}\right)\Gamma\left(\frac{n_{control}-2}{2}\right)}

where \Delta is the observed effect size, \Delta_{c} is the corrected estimate of \Delta, n_{control} is the control-group sample size, and \Gamma() is the gamma function.

Value

Vector of d values corrected for small-sample bias.

References

Hedges, L. V. (1981). Distribution theory for Glass’s estimator of effect size and related estimators. Journal of Educational Statistics, 6(2), 107–128. doi:10.2307/1164588

Examples

correct_glass_bias(delta = .3, nc = 30, ne = 30)