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Date:         Tue, 17 Jun 2003 21:47:20 -0400
Reply-To:     Jay Weedon <jweedon@EARTHLINK.NET>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Jay Weedon <jweedon@EARTHLINK.NET>
Organization: http://extra.newsguy.com
Subject:      Re: proc glm vs proc mixed help
Content-Type: text/plain; charset=us-ascii

On 17 Jun 03 15:16:11 GMT, raypass@ATT.NET (Ray Pass) wrote:

>I'm sending this out for a colleague. I am NOT a statistician, but I know >where to go for help.

>> Does anyone know how to calculate the confidence interval for the >>estimate using proc glm? I see how to calculate for the means by adding >>to the model statement, but not for the estimate. >> >> This is what I have so far: >> >>title2 "GLM p-values for &var"; >>proc glm data=gmean (where=(trt in (0,1))) ; >> class trt; >> model l&var = trt /solution ss3 ; >> estimate "ratio" trt -1 1; >>run; >> >> >>It's easy in proc mixed as there is an option to do so. See below. >>However, biostat doesn't want me to use proc mixed. >> >> >>title2 "Proc Mixed p-values for &var"; >>proc mixed data=gmean ; >> where trt in (0,1); >> class trt; >> model l&var = trt; >> estimate "Ratio" trt -1 1 / cl ; >> make "table" out=ratio estimate; >>run; >> >>Thanks for any tips you can give me.

"Biostat" can verify the following by RTFM for PROC MIXED, but AFAIK the method used by MIXED is the standard large-sample method:

Compute the t-statistic associated with the desired confidence level and the error df, and multiply this by the provided SE for the estimate. Then add/subtract this to/from the estimate value.

Example:

Estimate=4.8447 SE=1.7570 Error df=207.

2-tailed t-statistic for 207 df @ 95% CL = 1.9715.

1.9715*1.7570 = 3.4639.

CI = 4.8447 +/- 3.4639 = [ 1.3808, 8.3086 ]

JW


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