Data synthesis
We understand that there is no closed argument for preference for
use of fixed-effect or random-effects models. The random-effects
method incorporates an assumption that the different studies are
estimating different, yet related, intervention effects. This often
seems to be true to us and the random-effects model takes into
account differences between studies even if there is no statistically
significant heterogeneity. There is, however, a disadvantage to the
random-effects model. It puts added weight onto small studies
which often are themost biased ones. Depending on the direction
of effect, these studies can either inflate or deflate the effect size.
Therefore, we chose the fixed-effect model for all analyses. The
reader is, however, able to choose to inspect the data using the
random-effects model.