The Relationship Among the Standard Deviation of a Dataset and the   Standard Deviation and Average Two Part of This Set
  Meta-analysis involves combining summary information for related but independent studies. It uses different relationship to combine position measure as well as dispersion measures. The objective of this study is to discuss a relationship among the standard deviation of a data set and the standard deviation and mean of two part of this set. The problem was proposed in a systematic review with meta-analysis that combined two studies with missing data. 
Jose Fausto de Morais
stat.ME