one-step method of moment estimate of between random effect variance
implementation follows Kacker 2004 and DerSimonian and Kacker 2007 eq. 6
- Parameters:
- eff : ndarray
effect sizes
- var_eff : ndarray
variance of effect sizes
- weights : ndarray
weights for estimating overall weighted mean
- Returns:
tau2 – estimate of random effects variance tau squared
- Return type:
float