Comparing a single score to controls
Crawford and Howell (1998) propose a test that compares a single patient score to those obtained from a control group. This is a more convservative test that the usual one sample t-test because it assumes the patient score has a variance equal to that of the controls rather than treating this score as a constant with zero variance.
This test may be implemented using [attachment:crawford1.xls this spreadsheet] for raw data or Crawford's own [attachment:singlims.exe program] for summary data. See also [attachment:npsy.pdf here.]