Stats: if I know MEAN and SEM values of two groups, how can I get the MEAN and SEM of increased/decreased percentage compared between the two groups?

if I know MEAN and SEM values of two groups, how can I get the MEAN and SEM of increased/decreased percentage compared between the two groups? I know there is a formula, but I cannot find it now. 

28 June 2017 7,611 3 View