I am doing a logistic regression (binary DV) with 13 IV. As a first step I wanted to test the linearity assumption bw. the IVs and the logit. To do this I applied the Box Tidwell Method in SPSS by multiplying ln_independent * IV. Surprisingly all my independt variables turned out to be significant. I think this might be due to my large sample size. My single observations are weighted. Thus, my weighted N~800.000. My unweighted N=10.083. When using the unweighted not all variables are significant but still many of them. How can I solve this problem in SPSS? I have already tried just using a random subsample. However, I am uncertain whether I can just select a random subsample (SPSS Data > Select > Random).

  • Better than Box-Tidwell, model all your explanatory variables with splines. How to do that in spss I do not know. – kjetil b halvorsen Sep 14 at 12:57

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