Dear all, I have encountered a problem when perform stepwise regression. The dataset have more 9 independent variables, but 7 observation.
In R, before performing stepwise, a lm object should be given. fm <- lm(y ~ X1 + X2 + X3 + X11 + X22 + X33 + X12 + X13 + X23) However, summary(fm) will give: Residual standard error: NaN on 0 degrees of freedom Multiple R-Squared: 1, Adjusted R-squared: NaN F-statistic: NaN on 6 and 0 DF, p-value: NA In this situation, step() or stepAIC() will not give any useful information. I don't know why SAS could deal with this situation: PROC REG; MODEL y=X1 X2 X3 X11 X22 X33 X12 X13 X23/SELECTION=STEPWISE; RUN; Any help will be really appreciated. Wishes, Jinsong Zhao
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