A study that would otherwise be eligible is commonly excluded from a metaanalysis when the standard error of its treatment-effect estimator, or the estimate
of the variance of the outcomes, is not reported and cannot be recovered from the
available information. This is wasteful when the estimate of the treatment effect
is reported. We assess the loss of information caused by this practice and explore
methods of imputation for the missing variance. The methods are illustrated on
two sets of examples, one constructed specifically for illustration and another
based on a published systematic review.