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SPSS® 12.0 Command Syntax Reference

SPSS® 12.0 Command Syntax Reference

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NOMREG 1069<br />

FORWARD Forward entry. The variables (or interaction effects or nested effects) specified<br />

on FORWARD are tested for entry into the model one by one, based on<br />

the significance level of the likelihood-ratio statistic. The variable with the<br />

smallest significance level less than PIN is entered into the model, and the<br />

model is re-estimated. Model building stops when no more variables meet<br />

entry criteria.<br />

BSTEP Backward stepwise. As a first step, the variables (or interaction effects or<br />

nested effects) specified on BSTEP are entered into the model together and<br />

are tested for removal one by one. The variable with the largest significance<br />

level of the likelihood-ratio statistic, provided that the value is larger than<br />

POUT, is removed, and the model is re-estimated. This process continues until<br />

no more variables meet the removal criterion. Next, variables not in the<br />

model are tested for possible entry, based on the significance level of the<br />

likelihood-ratio statistic. The variable with the smallest significance level<br />

less than PIN is entered, and the model is re-estimated. This process repeats,<br />

with variables in the model again evaluated for removal. Model building<br />

stops when no more variables meet removal or entry criteria, or when the<br />

current model is the same as a previous model.<br />

FSTEP Forward stepwise. The variables (or interaction effects or nested effects)<br />

specified on FSTEP are tested for entry into the model one by one, based on<br />

the significance level of the likelihood-ratio statistic. The variable with the<br />

smallest significance level less than PIN is entered into the model, and the<br />

model is re-estimated. Next, variables that are already in the model are tested<br />

for removal, based on the significance level of the likelihood-ratio statistic.<br />

The variable with the largest probability greater than the specified POUT<br />

value is removed, and the model is re-estimated. Variables in the model are<br />

then evaluated again for removal. Once no more variables satisfy the removal<br />

criterion, variables not in the model are evaluated again for entry. Model<br />

building stops when no more variables meet entry or removal criteria, or<br />

when the current model is the same as a previous one.<br />

Examples<br />

NOMREG y BY a b c<br />

/INTERCEPT = INCLUDE<br />

/MODEL = a b c | BACKWARD = a*b a*c b*c a*b*c.<br />

• The initial model contains the intercept and main effects a, b, and c. Backward elimination<br />

is used to select among the two- and three-way interaction effects.<br />

NOMREG y BY a b c<br />

/MODEL = INTERCEPT | FORWARD = a b c.<br />

• The initial model contains the intercept. Forward entry is used to select among the main<br />

effects a, b, and c.<br />

NOMREG y BY a b c<br />

/INTERCEPT = INCLUDE<br />

/MODEL = | FORWARD = a b c.

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