Since I have some studies that reported the continuous outcome as change from baseline and others that reported it as end of value score, is it possible to include both?
More than likely, I would only use the change score. It provides the more meaningful value. The change score corrects for initial differences among your groups.
The Cochrane Handbook reports that you can combine change from baseline outcomes with final measurement outcomes "There is no statistical reason why studies with change-from-baseline outcomes should not be combined in a meta-analysis with studies with final measurement outcomes when using the (unstandardized) mean difference method in RevMan. In a randomized trial, mean differences based on changes from baseline can usually be assumed to be addressing exactly the same underlying intervention effects as analyses based on final measurements. That is to say, the difference in mean final values will on average be the same as the difference in mean change scores. If the use of change scores does increase precision, the studies presenting change scores will appropriately be given higher weights in the analysis than they would have received if final values had been used, as they will have smaller standard deviations."
This cannot be applied to network meta-analysis because? Are there statistical reasons for not combining these two types of results in a network meta-analysis?