Is this an error or not?

I am trying to fit a second order polynomial. I center and scale my predictors and fit the data using the lm function. I did summary(fit). For 3 of my variables, I got NA in all columns including estimate, p-value etc.

So, I am using R

I used the function lm as follows

fit1<- lm (y ~ x11+x22 + I(x11^2) +I(x22^2) +I(x11*x22) )


The output I got is:

Call:
lm(formula = y ~ x11 + x22 + I(x11^2) + I(x22^2) + I(x11 * x22))

Residuals:
Min       1Q   Median       3Q      Max
-0.33889 -0.21371  0.01898  0.15166  0.47933

Estimate       Std. Error         t value               Pr(>|t|)
(Intercept)         2.57956     0.05367            48.062               <2e-16 ***
x11             -0.13097        0.05329         -2.458                0.0194 *
x22                NA              NA                NA                NA
I(x11^2)             0.08673       0.03559        2.437            0.0204 *
I(x22^2)            NA            NA               NA                   NA
I(x11 * x22)        NA            NA              NA                  NA
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1


So, in short the variables x22, x22-square and interaction x1*x2 shows NA in all columns.

Is there an error to get NA or should I just be assuming that the predictors for which estimates are NA are just insignificant?

• Sure you can paste your output: copy it from the R window and paste it into your question-editing dialog as usual. Format it using the tools found across the top of the window.
– whuber
Commented Apr 10, 2013 at 17:53
• It would also be helpful to know what language you are using (is it indeed R?), as well as the code you used to generate your output. Commented Apr 10, 2013 at 18:14
• I added the output. Commented Apr 10, 2013 at 18:43
• What is the correlation coefficient between x11 and x22? Commented Apr 10, 2013 at 19:22

Did you get any warnings from lm?