x1
and x2 respectively mean the experimental group and the control group using mind map while s means the pooled
standard deviation).
To get the unbiased estimate of the standardized mean difference effect size, we calculate Hedge‘s
g( d
4n -9
3
g (1- ) ,n means the total number of participants in the experimental and control groups)( Lipsey and Wilson,
2001).
During the process, 18 studies of the original fifty eight (58) studies were discarded because there was insufficient
information for estimation of effect size.
To avoid loss of information, we decided to include all the effect sizes first.