IBM SPSS COMPLEX SAMPLES 19 manual Estimated Marginal Means

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Complex Samples General Linear Model

The parameter estimates are useful for quantifying the effect of each model term, but the estimated marginal means tables can make it easier to interpret the model results.

Estimated Marginal Means

Figure 19-9

Estimated marginal means by levels of Who shopping for

This table displays the model-estimated marginal means and standard errors of Amount spent at the factor levels of Who shopping for. This table is useful for exploring the differences between the levels of this factor. In this example, a customer who shops for him- or herself is expected to spend about $308.53, while a customer with a spouse is expected to spend $370.34, and a customer with dependents will spend $459.44. To see whether this represents a real difference or is due to chance variation, look at the test results.

Figure 19-10

Individual test results for estimated marginal means of gender

The individual tests table displays two simple contrasts in spending.

„The contrast estimate is the difference in spending for the listed levels of Who shopping for.

„The hypothesized value of 0.00 represents the belief that there is no difference in spending.

„The Wald F statistic, with the displayed degrees of freedom, is used to test whether the difference between a contrast estimate and hypothesized value is due to chance variation.

„Since the significance values are less than 0.05, you can conclude that there are differences in spending.

The values of the contrast estimates are different from the parameter estimates. This is because there is an interaction term containing the Who shopping for effect. As a result, the parameter estimate for shopfor=1 is a simple contrast between the levels Self and Self and Family at the level From both of the variable Use coupons. The contrast estimate in this table is averaged over the levels of Use coupons.