two-tailed vs one-tailed t-test

two-tailed vs one-tailed t-test

two-tailed
- less specific, two directions, eg. null: male different from female?

one-tailed
- more specific, more power, one direction only, eg. null: male higher than female?

http://www.ats.ucla.edu/stat/mult_pkg/faq/general/tail_tests.htm