Date:         Thu, 20 Apr 2006 05:53:56 -0700
Reply-To:     Yung-jui Yang <yungjui@GMAIL.COM>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         Yung-jui Yang <yungjui@GMAIL.COM>
Organization: http://groups.google.com
Subject:      Re: SAS macro for testing moderation/interaction
Comments: To: sas-l@uga.edu
In-Reply-To:  <BAY103-F32A66653F9A71C9754E14CB0BA0@phx.gbl>
Content-Type: text/plain; charset="iso-8859-1"

Hi David,

> If you have two continuous regressors, then ODS Statistical Graphics does something else for you.  But if you have two continuous regressors, then you ought to be using PROC REG (or something like it) instead of PROC GLM.

True, but ODS Graphics isn't cure-all. As shown in
http://support.sas.com/onlinedoc/913/getDoc/zt/statug.hlp/reg_sect50.htm
ODS Graphics in PROC REG doesn't plot interactions, whereas my macros
can plot them easily.

> Procs like PROC IML take a *massive* hit because they're trying to store everything in RAM instead of using the I/O sub-systems that are the underpinnings of the stat and base procs.  So, as your data set grows, the whole system slows down, and the time to complete the entire thing increases. ... Especially if it takes 4 hours one way and *40* hours your way.

True, but you misunderstand my macros. I do use PROC IML in them but I
use it for very low-RAM-consuming computation.  In fact, the PROC IML
there uses the output dataset of PROC REG, which would be a constant
matrix, typically a 17-variable by 6-observation dataset, for either
25-case dataset or 250,000-case dataset. In other words, if it took 4
hours for PROC REG, it'd also take 4 hours for my macros too.

> A really important aspect here is the choice of the proc.  ... For example, evaluation of higher-order interactions needs to be done in conjunction with appropriate model diagnostics, including diagnostic plots, so someone can tell whether the errors are normal, the residuals are independent, the errors are
identically distributed, the data lack outliers and/or leverage points,
...

True, and these are what I agree ODS Graphics is good at.

Best,
Yung-jui