Re: inclusion of covariates with $PRIOR

Dear Anna, The times I have used SCM in combination with a frequentist prior, it has been only to test if a new population is different (i.e. the data used to generate the prior were all of a different population, e.g. healthy volunteers and other indications than the currently-investigated population. Or something similar where the covariate value is a nominal level which was not present in the data used to generate the prior). To use SCM in combination with NWPRI in that situation is straightforward. With regards to your first question. If you use a prior only to support the estimation of this specific covariate coefficient (no prior on other parameters), then you do not need to center around the same covariate value. The point estimate for the covariate coefficient will be the same, regardless of how you center these covariate models (but standard errors, correlation between estimates and the covariance matrix as a whole will be different depending on how you center). However, with prior across all model parameters, it would be important to center across the same covariate value, since the population typical value is with regards to this (e.g. the population typical clearance for a subject with 70 kg body weight). Maybe this is what Gisleskog et al. were referring to? With regards to model selection with a prior on all available parameters this is not as straightforward. If your prior is a full model (including all covariates that you want to test in SCM), then in principle using prior on all fixed effects would be possible. But due to correlation between the estimates in your prior you could end up leaving a covariate out of the model, in a way that would not have happened in a combined analysis. An alternative may be to have separate priors for each model you test, but I do not think there is any automated software to support that procedure. If you have access to the data used to generate the prior, it may be easier to combine all data, rather than using a frequentist prior. I suspect this is not possible in your case, since you ask these questions? Best regards Jakob Jakob Ribbing, Ph.D. Senior Consultant, Pharmetheus AB Cell/Mobile: +46 (0)70 514 33 77 [email protected] www.pharmetheus.com http://www.pharmetheus.com/ Phone, Office: +46 (0)18 513 328 Uppsala Science Park, Dag Hammarskjölds väg 36B SE-752 37 Uppsala, Sweden This communication is confidential and is only intended for the use of the individual or entity to which it is directed. It may contain information that is privileged and exempt from disclosure under applicable law. If you are not the intended recipient please notify us immediately. Please do not copy it or disclose its contents to any other person.