Inverse-variance weight ($w_i=v_i^{-1}$)

A weight $w_i=1/v_i$ gives more weight to a more precise estimate. In random-effects meta-analysis the variance of the corresponding marginal distribution is $v_i+{\tau }^2$, giving weight $(v_i+{\tau }^2{)}^{-1}$. A percentage weight divides the individual weight by the sum of all weights.