Suppose the model contains explanatory effects. For the
th observation, let
be the estimated probability of the observed response. The three criteria displayed by the SURVEYLOGISTIC procedure are calculated as follows:
log likelihood:
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where and
are the weight and frequency values, respectively, of the
th observation. For binary response models that use the events/trials syntax, this is equivalent to
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where is the number of events,
is the number of trials, and
is the estimated event probability.
Akaike information criterion:
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where is the number of parameters in the model. For cumulative response models,
, where
is the total number of response levels minus one, and
is the number of explanatory effects. For the generalized logit model,
.
Schwarz criterion:
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where is the number of parameters in the model. For cumulative response models,
, where
is the total number of response levels minus one, and
is the number of explanatory effects. For the generalized logit model,
.
The 2 log likelihood statistic has a chi-square distribution under the null hypothesis (that all the explanatory effects in the model are zero), and the procedure produces a
-value for this statistic. The AIC and SC statistics give two different ways of adjusting the
log likelihood statistic for the number of terms in the model and the number of observations used.