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SPSS® 12.0 Command Syntax Reference

SPSS® 12.0 Command Syntax Reference

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680 GLM: Repeated Measures<br />

GLM Variable List<br />

The list of dependent variables, factors, and covariates must be specified first.<br />

• WSFACTOR determines how the dependent variables on the GLM variable list will be<br />

interpreted.<br />

• The number of dependent variables on the GLM variable list must be a multiple of the<br />

number of cells in the within-subjects design. If there are six cells in the within-subjects<br />

design, each group of six dependent variables represents a single within-subjects variable<br />

that has been measured in each of the six cells.<br />

• Normally, the number of dependent variables should equal the number of cells in the<br />

within-subjects design multiplied by the number of variables named on the MEASURE<br />

subcommand (if one is used). If you have more groups of dependent variables than are<br />

accounted for by the MEASURE subcommand, GLM will choose variable names to label<br />

the output, which may be difficult to interpret.<br />

• Covariates are specified after keyword WITH. You can specify constant covariates. Constant<br />

covariates represent variables whose values remain the same at each within-subjects level.<br />

Example<br />

GLM MATH1 TO MATH4 BY METHOD WITH SES<br />

/WSFACTOR=SEMESTER 4.<br />

• The four dependent variables represent a score measured four times (corresponding to the<br />

four levels of SEMESTER).<br />

• SES is a constant covariate. Its value does not change over the time covered by the four<br />

levels of SEMESTER.<br />

• Default contrast (POLYNOMIAL) is used.<br />

WSFACTOR Subcommand<br />

WSFACTOR names the within-subjects factors, specifies the number of levels for each, and<br />

specifies the contrast for each.<br />

• Presence of the WSFACTOR subcommand implies that the repeated measures model is<br />

being used.<br />

• Mauchly’s test of sphericity is automatically performed when WSFACTOR is specified.<br />

• Names and number levels for the within-subjects factors are specified on the WSFACTOR<br />

subcommand. Factor names must not duplicate any of the dependent variables, factors, or<br />

covariates named on the GLM variable list. A type of contrast can also be specified for<br />

each within-subjects factor in order to perform comparisons among its levels. This<br />

contrast amounts to a transformation on the dependent variables.<br />

• If there are more than one within-subjects factors, they must be named in the order corresponding<br />

to the order of the dependent variables on the GLM variable list. GLM varies the<br />

levels of the last-named within-subjects factor most rapidly when assigning dependent<br />

variables to within-subjects cells (see the example below).<br />

• The number of cells in the within-subjects design is the product of the number of levels<br />

for all within-subjects factors.

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