I am looking for the formula for the confidence interval for the difference in means in a one sample t-test. I have only been able to locate the formula for a two sample t-test. Let me give an example: I have the following ten scores 10,12,13,11.5,9,11,11.1,11.9,12.1,9.3. I want to know if the means of these scores is significantly different from my population mean of 11.5. When I conduct a one sample t-test in SPSS I get the following results" tobtained=-10.776 SIG(ie.P)=.000 95% CI of the difference=-.5.3363 to -3.4837. I know how SPSS calculated Totained and P but not how it calculated 95% CI of the difference. This 95% CI of the difference is not the same as the CI for the mean. The CI for the mean I can obtain by CI =x-bar plus or minus t* S/(sqrt N). The confidence interval in this case is: 10.16,12.01. I get the same result if I calculate this in SPSS. So my question is: what is the formula for the CI of the difference which SPSS produces? How do I get that range. I do not want the CI for the mean. Thanks.