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Date:         Fri, 12 Dec 2008 11:37:57 -0600
Reply-To:     Mary <mlhoward@avalon.net>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Mary <mlhoward@AVALON.NET>
Subject:      Re: experimental design question
Comments: To: "Swank, Paul R" <Paul.R.Swank@UTH.TMC.EDU>
Content-Type: text/plain; charset="iso-8859-1"

Paul,

It sounds to me like it is measured; presumably at baseline and at followup (time of assesment of improvement or not).

I'd be interested in your thoughts on what sort of model this would be.

-Mary ----- Original Message ----- From: Swank, Paul R To: SAS-L@LISTSERV.UGA.EDU Sent: Friday, December 12, 2008 11:34 AM Subject: Re: experimental design question

It looks like you are positing a mediation model but it is unclear about X enzyme level. Is this measured or manipulated?

Paul R. Swank, Ph.D Professor and Director of Research Children's Learning Institute University of Texas Health Science Center Houston, TX 77038

-----Original Message----- From: SAS(r) Discussion [mailto:SAS-L@LISTSERV.UGA.EDU] On Behalf Of duo wan Sent: Friday, December 12, 2008 11:11 AM To: SAS-L@LISTSERV.UGA.EDU Subject: experimental design question

Hi All,

Could someone help me with a quick question for experimental design?

The design is a simple one: 1 New therapy has better treatment results than old therapy. 2. high X enzyme level is associated with better treatment results.

Test hypothesis: New therapy is better probably because it produces higher X enzyme level.

"New therapy=>higher X enzyme level=>better treatment results". One corresponding design solution: Group1: New therapy + nothing (higher X) Group2: New therapy+X enzyme inhibitor(lower X) Group3: Old therapy+nothing (lowest X level)

can ANOVA answer "New therapy=>higher X enzyme level=>better treatment results" by comparing 3 groups in term of treatment results?

I think it is more than ANOVA because X enzyme level is an intermediate outcome, not just explanatory variable. or This is question that should be answered by causal model (direct, indirect effects,surrogate outcome)?

Anyone could help me with some references with similar design?

thanks,

Vincent


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