[R] plotting residuals/error message

[John Fox]

Dear Jason,

Your suspicion is correct: the cases with NAs in either ft_dpc_r or pid_x
are absent from the residuals but not from pid_x. 

There are several ways to deal with this problem, but one straightforward
way is to use na.exclude in place of the default na.omit in the call to lm,
as in lm(ft_dpc_r~pid_x, na.action=na.exclude). Then residuals() will pad
out the values it returns with NAs.

I hope this helps,
 John

-----------------------------------------------
John Fox, Professor
McMaster University
Hamilton, Ontario, Canada
http://socserv.socsci.mcmaster.ca/jfox/



> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of Gainous,Jason
> Sent: Saturday, March 15, 2014 1:42 PM
> To: r-help at r-project.org
> Subject: [R] plotting residuals/error message
> 
> I am trying to plot the residuals from a linear model and I get the
> following error message: Error in xy.coords(x, y, xlabel, ylabel, log)
> :  'x' and 'y' lengths differ. The outcome is a continuous variable and
> the explanatory variable is ordinal. My immediate suspicion was that it
> had something to do with missing values. Each variable has missing
> values coded as NA. I can't figure it out. Please help. Thanks.
> 
> > obama.mod = lm(ft_dpc_r~pid_x)
> > summary(obama.mod)
> 
> Call:
> lm(formula = ft_dpc_r ~ pid_x)
> 
> Residuals:
>     Min      1Q  Median      3Q     Max
> -89.271 -14.783   0.729  10.729  84.193
> 
> Coefficients:
>             Estimate Std. Error t value Pr(>|t|)
> (Intercept) 101.5155     0.5797  175.12   <2e-16 ***
> pid_x       -12.2441     0.1411  -86.76   <2e-16 ***
> ---
> Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
> 
> Residual standard error: 22.85 on 5876 degrees of freedom
>   (36 observations deleted due to missingness)
> Multiple R-squared:  0.5616, Adjusted R-squared:  0.5615
> F-statistic:  7528 on 1 and 5876 DF,  p-value: < 2.2e-16
> 
> > plot(pid_x, resid(obama.mod), ylab = "Model Residuals")
> Error in xy.coords(x, y, xlabel, ylabel, log) :
>   'x' and 'y' lengths differ
> 
> 
> Jason Gainous, Ph.D.
> Associate Professor
> Department of Political Science
> University of Louisville
> 203 Ford Hall
> Louisville, KY 40292
> (502) 852-1660
> Homepage: https://louisville.academia.edu/JasonGainous
> 
> 
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