StataCorp LP. (2005). Stata user's guide: Release 9. StataCorp LP.
Cita Chicago (17th ed.)StataCorp LP. Stata User's Guide: Release 9. College Station, Tex: StataCorp LP, 2005.
Cita MLA (9th ed.)StataCorp LP. Stata User's Guide: Release 9. StataCorp LP, 2005.
Atenció: Aquestes cites poden no estar 100% correctes.