Unit of analysis issues. The level at
which randomization occurred in each of the RCTs was taken into account
so that the number of observations coincided with the number of
randomized units. If we included clinical trials with multiple arms and
one arm was considered more than once in the same comparisons (e.g.,
different dosing schedules of the same therapeutic agent compared to the
same control group), we combined all relevant treatment arms in a single
group and compared with the control to avoid double counting of
participants in control
groups.
The statistical method usually used to combine the
results of multiple studies is to weight them by the amount of
information they provide (more specifically, by the inverse variances of
their effect estimates). Those trials that contribute more weight are
mentioned.