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$\begingroup$ Thank you for your answer. I am content with using raw years if that is the accepted approach thanks to rms tools. However I still do not completely understand why Aiken and West recommend centering the continuous variable in the case of an interaction in chapter 3 of their 1991 book, even though both centered and uncentered models are mathematically equivalent. Regarding the earlier years in the test set, if we set them to the last year available in the training set, would this approach let us keep the earlier datapoints via bypassing the backwards extrapolation? Or would this introduce bias? $\endgroup$

Çağan Kaplan
– Çağan Kaplan

2026-03-31 20:17:54 +00:00
Commented 9 hours ago
$\begingroup$ @ÇağanKaplan without centering, calculations for interaction (product) terms can involve fairly extreme numeric values, which was perhaps more of a practical issue in 1991 than it is today. It would be dangerous to use your pre-2004 test data to evaluate your SEER model. Setting the corresponding dates of earlier test cases to 2004 (as you seem to propose) would assume that the clinical/outcome situation for those earlier cases was the same as in 2004. That seems unlikely. as IMRT started being widely adopted in the late 1990s. $\endgroup$

EdM
– EdM

2026-03-31 20:42:10 +00:00
Commented 9 hours ago

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