Many Thanks Paul! Your explanation cleared up my confusion.
kindest regards,
Clint
On 7 Jul 2004 at 17:02, VISINTAINER PAUL wrote:
> Clint,
>
> I think your confusion about the tests of homogeneity stems from what is
> being tested. A test of homogeneity can be use to test whether the
> exp-dis ORs differ over a third variable (effect modification) or
> whether the ORs differ over several levels of an exposure
> variable--regardless of whether a third variable is present.
>
> -tabodds- allows you to examine the effect of an exposure that is
> measured at more than 2 levels, e.g., 4x2; a 4-level exposure crossed
> with a 2-level disease state. The real advantage of the -tabodds-
> command is that the score test helps us to determine whether there is a
> "dose-response" relationship. The test of homogeneity can be used to
> detect a "threshold" of exposure. This test, though, still is based on
> two variables. (-tabodds- allows adjustment for a third variable, but
> not a test of interaction). The main thing to remember is to use
> -tabodds- to examine a multi-level exposure.
>
> The test of homogeneity in the -cc, by()- command is testing effect
> modification. In this case, the test overlaps the -mhodds- command,
> which does the same thing. We use this to address the question of
> whether the exp-dis ORs are the same over strata of a third variable.
> Obviously, if the test of homogeneity indicates that the ORs do differ
> over strata of the third variable (i.e., the test is significant), using
> a single statistic like the MH-odds to summarize the data may be quite
> misleading.
>
> pfv
>
>
> ______________________________
> Paul F. Visintainer, PhD
> Professor and Program Director
> Health Quantitative Sciences
> School of Public Health
> New York Medical College
>
> -----Original Message-----
> From: [email protected]
> [mailto:[email protected]] On Behalf Of
> [email protected]
> Sent: Wednesday, July 07, 2004 2:31 PM
> To: [email protected]
> Subject: st: -tabodds- versus -cc-
>
> Hello Statalisters --
> I am using Intercooled Stata, version 8.2. I hope someone can
> clarify the use of -tabodds- versus -cc- when determing whether
> a Mantel-Haenszel (MH) odds ratio is appropriate. As I
> understand it (and please feel free to correct me if my
> understanding is misguided), the first step in determining
> whether a MH odds ratio is appropriate is to generate odds
> ratios for each group via -cc case_var exp_var, by(varname)-
> then to follow this command with -tabodds case_var exp_var-
> wherein I refer to the 'Test of Homogeneity (equal odds)' for
> confirmation (or not) of whether a MH odds ratio is
> appropriate. The Stata 7 reference manual (vol 1, pg 467),
> however, indicates that I ought to refer only to the -cc-
> output and its 'Test of Homogeneity (M-H)' in determining
> whether a MH odds ratio is appropriate. Can anyone clarify?
>
> As always, any suggestions are appreciated!
>
> Many Thanks,
> Clint Thompson
>
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