PAIRDATA: Stata module to create paired datasets from individual-per-row data

pairdata is a command to create paired datasets from individual-per-row data, specifically useful for twin/sibling data. Three paired datasets are created: single.dta - single entered file with unique pair combinations; singlerand.dta- a single entered file with unique pair combinations controlling for any type of order effect; double.dta - a double entered file with all possible pair combinations. Two new variables are also created; famcount - the number of members in each family, nsibpair - the number of pairs per family. It is also possible to specify variables that are family specific and so will appear unpaired.