# Re: [R] NA handling with lm

From: Petr Pikal <petr.pikal_at_precheza.cz>
Date: Fri 29 Jul 2005 - 02:59:58 EST

Hallo

> Hi,
> I have a problem that is hopefully easily solvable, but I dont find
> the clue in the documentation. I am examining a linear model. One of
> the variables has NA values. Even though na.action=na.omit, i get NA
> as results for this variable. Can I use lm in such a case to get
> estimates? Or do I have to do some form of imputation before doing so?
> Here is the call and the results, hope you can help. Best regards,
> Andreas
> ----------------------------------------------------------------------
> ----------------------- lm(formula = ESSIK ~ ALTER + as.factor(S2) +
> as.factor(S15A) +
> as.factor(S8) + as.factor(LAND) + as.factor(S18B) +
> as.factor(BERUF) + as.factor(KIRCHE) + as.factor(H_EINKOM) +
> as.factor(PARTNERS), na.action = na.omit)
>
> Residuals:
> Min 1Q Median 3Q Max
> -17.0675 -2.0151 0.4267 2.7644 9.7333
>
> Coefficients: (2 not defined because of singularities)

Problem is not in NA handling but that some of your coeficients can be represented as linear combination of other coeficients. You have to omit them.

HTH
Petr

> Estimate Std. Error t value Pr(>|t|)
> (Intercept) 23.755915 1.844110 12.882 < 2e-16 ***
> [...]
> as.factor(BERUF)7 -1.236836 0.701323 -1.764 0.077942 .
> as.factor(KIRCHE)1 -0.811751 0.237699 -3.415 0.000649 ***
> as.factor(H_EINKOM)2 NA NA NA NA
> as.factor(H_EINKOM)3 NA NA NA NA
> as.factor(PARTNERS)1 2.057070 0.342546 6.005 2.23e-09 ***
>
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