how to derive difference in percentage change from baseline (log-transformed)

CL52 — Thu, 13 Oct 2022 19:22:23 GMT

Dear all,

I struggled to figure out how to derive SD and confidence interval for difference between groups in percentage change from baseline, analyzed in log-transformation.

In proc mixed, I have [log(Post) - log(BL)] as response. and treatment as indepent variables, visit, and treatment by visit interaction. So I know, the coefficient beta1 for treatment (and beta0 as intercept), I can transform back to get the percentage change (exp(beta0+beta1) - 1)*100%.

However what I am interested in is the difference between the group.

[exp(beta0+beta1)-1] - [exp(beta0)-1] = exp(beta0)*(exp(beta1) - 1)

How can I derive the SD and CI of the above with the LSmeans output?

Any reference I can go to?

Many thanks!

Carrie

Re: how to derive difference in percentage change from baseline (log-transformed)

StatDave — Thu, 13 Oct 2022 20:18:33 GMT

The LSMEANS statement cannot be used to estimate or test nonlinear combinations of model parameters. For that, you can use the NLEST macro.

topic how to derive difference in percentage change from baseline (log-transformed) in Statistical Procedures

how to derive difference in percentage change from baseline (log-transformed)

Re: how to derive difference in percentage change from baseline (log-transformed)