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Mar 28, 2023 at 1:34 comment added David B age + age_slope_change is the same as (age-25):age_bin + age. If you recode age_bin as 0 and 1 then (age-25):age_bin is literally the same as age_slope_change.
Mar 27, 2023 at 20:30 vote accept LucaS
Mar 27, 2023 at 20:30 comment added LucaS Thanks - I will accept your answer as it's the closest match to my question. I still couldn't get those two parameterisations to match up though - age + age_slope_change and (age-25)*age_bin.
Mar 27, 2023 at 15:04 comment added David B Actually no! They're similar, but there's a very important difference. See the edit to my original answer.
Mar 27, 2023 at 15:04 history edited David B CC BY-SA 4.0
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Mar 26, 2023 at 21:53 comment added LucaS Thanks @DavidB. This is probably the closest to helping me understand my problem. It's a different parameterisation. What I don't still fully get is why the estimates from the two models aren't the same (they are close but not exactly the same). Isn't a model with age + age_slope_change (where age_slope_change = 0 before chngpt and (age-chngpt) after), essentially the same as a model with age * age_bin (where age_bin = 0 before chngpt and 1 after)?
Mar 24, 2023 at 15:01 history answered David B CC BY-SA 4.0