If I have stratified data in SPSS, how does that affect the margin of error calculation?

Stratified sampling can *reduce* the margin of error compared to simple random sampling, assuming the strata are appropriately defined. However, SPSS doesn't directly calculate a margin of error specifically for stratified samples within the standard Descriptive Statistics or T-Test procedures. You'll need to calculate the weighted standard error and then the margin of error based on the stratified sample design using formulas available in statistical textbooks or online resources. SPSS's Survey procedures can handle more complex sampling designs and provide appropriate standard errors.