RE: Centering (was Re: Missing covariates)

From: "KOWALSKI, KENNETH G. [PHR/1825]" <kenneth.g.kowalski@pharmacia.com> Subject: RE: Centering (was Re: Missing covariates) Date: Mon, 2 Jul 2001 15:47:51 -0500 Nick, The advantages of centering are numerical not statistical. That is, convergence to the minimum ELS should be faster using centering than without. However, both should lead to the same minimum value of the ELS and the same parameter estimates after adjusting for the centered value. When there is numerical instability centering can often help. It is good to do some sort of centering although it may not be necessary to do it at the precise center of your data. I agree with you that using standards such as wt=70 kg, age=40 yrs, etc. is convenient. Ken