[R] R ANOVA gives diferent results than SPSS

Peter Ehlers ehlers at ucalgary.ca
Thu Feb 11 21:50:07 CET 2010

Comment inserted below.

Greg Snow wrote:
> A couple of possibilities:
> The data is not the same, e.g. something in the file was interpreted
differently by the 2 programs, one of the programs may have stopped
reading at an unrecognized value, while the other skipped it and went
on. Or it used to be common to encode missing values as -999, if one
program recognizes that as missing, but you did not tell the other one
too, then it could treat that as a legitimate value.
> The model is not the same, e.g. one program may be interpreting your
grouping variable as a continuous variable and the other as categorical,
which would result in 2 very different models and outcomes.

My money is on this one. I'm guessing that there is a grouping
variable coded with levels 1,2,3,etc, and that R is not being
told that this is a grouping variable.


> If you show us your data/code/output as has been requested, then we
may be able to tell which it is. Without that information you are
expecting either R or the members of the list to read your mind. I keep
making notes to my future self to use the timetravel package (not
written yet, that's why I need my future self to use it) to send a copy
of the esp package (also not written yet) back in time to me so I can
use it for situations like this. But so far that has not worked (maybe
my future self is even more lazy than my present self, or my near future
self does something to offend my far future self enough that he is
unwilling to do this small favor for my current past self, darn, either
way means I should probably do better on the diet/exercise).
> The short version of the above rambling is that we want to help, but
cannot help you until you help us to help you. Show us your
data/code/output (or data/code/output for simulated/example data if you
can't show your real data).


Peter Ehlers
University of Calgary

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