Dear Jamie, It worked. Thank you so much.Dear Jens, In the F1 help file of Epi Analysis, please incorporate it separately; The steps for Unpaired “t” test (which “means command” generates between two independent sample), In the help file we only have this line for (Unpaired) “t” test, MEANS BP /by=SMOKE The Paired “t” test steps which Jamie has described, should also be included.. Example:* paired t-test on variables x1 and x2 gen xdiff=x1-x2means xdiff /t Our Epidata Entry and Analysis manual is developing. The Command reference is the heart of any User Manual. Another manual of (www.tbrieder.org) is also very useful but Command reference section is required. Our list has vast searchable resource (compilation of last 12 years) of “Solutions” for the common problems, the users have encountered. Hence let us work on a standard Reference manual of Epidata Entry and Analysis. Of course, the future challenges are USER manuals of EntryClient and manager also. With best wishes and regards, Dr. Shavinder Singh