1- Is it reasonable to trace a trend line of the evolution of a parameter over time from the pooling of different studies, each of which do not contain all time points? See the pictures for exemple: the forest plot picture shows all the different studies' contribution to each time point. Then I compute a graph from the mean +- SD of each time point, with a trend line. Is this heresy?

2- If this is acceptable, can we (and how do we) compare these time point changes among each other?

Thanks!