Date:         Tue, 12 Aug 2008 12:26:07 -0500
Reply-To:     "./ ADD NAME=Data _null_," <iebupdte@GMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "./ ADD NAME=Data _null_," <iebupdte@GMAIL.COM>
Subject:      Re: interpreting ESTIMATE output GLM
Comments: To: cooch17@nospamverizon.net
In-Reply-To:  <48A1BBEB.7010907@NOSPAMverizon.net>
Content-Type: text/plain; charset=ISO-8859-1

1). Fit the liner model with GLM, no class statement.

    model x = trt;

2 ) figure out what needs to be modified for estimate statement to
estimate the slope.

   estimate 'linear' trt -2 -1 0 1 2 / divisor=10;

If I was smart I would not need step 1.


On 8/12/08, cooch17@nospamverizon.net <cooch17@nospamverizon.net> wrote:
> Suppose I have a single-classification ANOVA, where the sample means
> show ordinal trend among successive levels. I construct a CONTRAST to
> test for trend, in the usual manner. Fine - but I'm puzzled how to
> interpret the parameter output from ESTIMATE (for the same contrast).
>
> For example, consider the following code snippet:
>
> data test;
>
>   do trt=1 to 5;
>
>     do i=1 to 5000;
>
>     x=normal(0)*1.25+trt;
>
>        output;
>
>      end;
>
>   end;
>
>
>
> proc glm;
>
>  class trt;
>
>    model x=trt / ss3;
>
>     lsmeans trt;
>
>     contrast 'linear' trt 2 1 0 -1 -2;
>
>     estimate 'linear' trt 2 1 0 -1 -2;
>
>     estimate '1 v 2' trt 1 -1 0 0 0;
>
>     estimate '2 v 3' trt 0 1 -1 0 0;
>
>     estimate '3 v 4' trt 0 0 1 -1 0;
>
>     estimate '4 v 5' trt 0 0 0 1 -1;
>
> run;
>
> So, 5 treatment levels, linear increase of the treatment mean by 1 for
> each level of trt. So, in fact, the 'slope' of the increase in the
> treatment effect is 1 (confirmed by each of the paired estimate
> statement contrasting successive treatment means). However, the output
> from the linear ESTIMATE is (for a given simulated sample) something like
>
> estimate:  -9.9968
> SE: 0.056
>
> So, rounding off the estimate to -10 (which is what it should be...
>
> (2)(1)+(1)(2)+(0)(3)+(-1)(4)+(-2)(5) = 10
>
> how do I interpret it? It clearly isn't the slope of the change in
> treatment effect (even if I take it and divide it by 5 - the number of
> levels of the treatment -  it still isn't). While I *know* this is an
> acceptable approach to testing significance of a trend, I also need to
> estimate the slope of the trend. So, how to go from what ESTIMATE gives
> me, to what I actually want/need.
>
> Pointers to the obvious?
>
> Thanks in advance.
>