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When I run a binary logistic regression using SPSS 19, the program can analyse seven covariates, but consistently omits the eighth. This occurs regardless of which covariate it is. Is this a limitation of this version of the software, or can someone suggest what I may be doing wrong?

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Are your 8 covariates perhaps a set of mutually exclusive dummy variables? – Andy W Aug 8 '12 at 2:24
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If you post your code, someone might be able to help. I don't use SPSS myself, but this can't be a limitation of the software, that would be stupid and the makers of SPSS are not stupid. – Peter Flom Aug 8 '12 at 11:26
I have SPSS 19.0.0 and don't have this problem. May be you are selecting one of the model selection procedures? – RioRaider Aug 8 '12 at 13:51
SPSS appears to be smart enough to exclude the 8th covariate if the 8 covariates are from a set of mutually exclusive dummy variables as noted by @AndyW. – RioRaider Aug 8 '12 at 14:00
Thanks everyone. I think what has happened is that one of the variables (who pays for car running costs) is a complete subset of another (vehicle access), so one or other is omitted if I run them both. Your comments have been helpful. – Margaret Aug 10 '12 at 0:38
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