How do I calculate the mean and SD of change using mean and SD of baseline and follow up results? I need mean and standard deviation of change from baseline to follow-up for inclusion in a meta-analysis.
Some papers present the findings as baseline mean, SD and follow-up mean, SD for both groups. How do I calculate this?
I also have sample size information.
Treatment_baseline Treatment_followup Treatment_change
     mean_x +/- SD      mean_y +/- SD          ? +/- ?

 A: In some areas, mean change is the best approach because the correlation between baseline and follow-up is high (e.g., r > 0.5) [1]. Besides, empirical evidence suggests that, overall, at the meta-analysis level, there is little difference in using mean at follow-up vs mean change from baseline.
There are several ways to approximate the mean change from baseline based on baseline and follow-up values. See formula is given here (you will need to "guestimate" a correlation coefficient, or estimate it from other studies that have individual patient data or report mean at baseline, mean at follow-up and mean change:
https://handbook-5-1.cochrane.org/chapter_16/16_1_3_2_imputing_standard_deviations_for_changes_from_baseline.htm
[1] da Costa, B. R., Nüesch, E., Rutjes, A. W., Johnston, B. C., Reichenbach, S., Trelle, S., ... & Jüni, P. (2013). Combining follow-up and change data is valid in meta-analyses of continuous outcomes: a meta-epidemiological study. Journal of clinical epidemiology, 66(8), 847-855.
