I'm attempting to select a model using stepAIC. I want to use a forward
selection procedure. I have specified a "scope" option, but must not be
understanding how this works. My results indicate that the procedure begins
and ends with the "full" model (i.e., all 17 independent variables)...not
what I expected. Could someone please point out what I'm not understanding?
My code is below.
Thanks.
Marc
> m1.stepFwd <- stepAIC(m1, direction="forward",
+ scope=list(upper=~age.refc.fo + dusz.cat.fo +
+ ed.du.f + emp.ref.f + geodist3.f + has.fone.f +
+ healthdu.f + help.du.f + inc.ref.f + maj.act.f +
+ marryref.f + msa.stat.f + regionrf.f + r.e.ref.f +
+ sex.ref.f + type.psu.f + urb.stat.f, lower=~1))
Start: AIC= 4752.19
response ~ age.refc.fo + dusz.cat.fo + ed.du.f + emp.ref.f +
geodist3.f + has.fone.f + healthdu.f + help.du.f + inc.ref.f +
maj.act.f + marryref.f + msa.stat.f + regionrf.f + r.e.ref.f +
sex.ref.f + type.psu.f + urb.stat.f
>
> m1.stepFwd$anova
Stepwise Model Path
Analysis of Deviance Table
Initial Model:
response ~ age.refc.fo + dusz.cat.fo + ed.du.f + emp.ref.f +
geodist3.f + has.fone.f + healthdu.f + help.du.f + inc.ref.f +
maj.act.f + marryref.f + msa.stat.f + regionrf.f + r.e.ref.f +
sex.ref.f + type.psu.f + urb.stat.f
Final Model:
response ~ age.refc.fo + dusz.cat.fo + ed.du.f + emp.ref.f +
geodist3.f + has.fone.f + healthdu.f + help.du.f + inc.ref.f +
maj.act.f + marryref.f + msa.stat.f + regionrf.f + r.e.ref.f +
sex.ref.f + type.psu.f + urb.stat.f
Step Df Deviance Resid. Df Resid. Dev AIC
1 NA NA 5311 4660.192 4752.192
>
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