On Oct 7, 2010, at 4:41 PM, Peter Dalgaard wrote:
On 10/07/2010 08:24 PM, David Winsemius wrote:
On Oct 7, 2010, at 2:21 PM, Barth B. Riley wrote:
Dear list
I would like to compute a Mantel-Haenszel chi-square in which the
matching variable is a continuous variable. The MH chi-square is
used to assess the relationship between two categorical variables at
each level or strata defined by a third variable. Specifically I
would like to know if there is a straightforward way to divide the
matching variable into levels, in which each level has a minimum of
20 cases. Any information would be greatly appreciated.
Why? What makes you think matching would be valuable? (...or even
valid, for that matter.)
What makes you think he has a choice?
He was asking for advice about how to construct matching strata using
a continuous variable.
Matching is generally part of the
design and data may already have been collected...
But it sounded as though the matching was not a "done deal" (since the
strata had not yet been defined) and I was attempting to clarify the
purposes.
For small-strata analyses look at clogit() in survival package. For
cutting a continuous variable into roughly equal-sized strata use a
combination og cut() and quantile() or (AFAIR) cut2() from one of
Frank
Harrell's packages.
I replied offlist with such advice.
Finally, Breslow+Day in their classic book on
case-control studies suggest replacing matched analysis by ordinary
logistic regression with the effect of the matching variable modeled
by
a suitably high-order polynomial.
Exactly. Breslow and Day is my preferred citation for pitfalls of
matching. Neither matching nor covariate adjustment should be
performed when there is a causal ( or other ) dependence of the
adjustment covariate and the predictor of interest. The classic
example of an erroneous use of matching in the medical field was
publication that described adjustment for menopausal bleeding in
analyses of potential causes of uterine cancer.
--
David.
--
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Phone: (+45)38153501
Email: [email protected] Priv: [email protected]
David Winsemius, MD
West Hartford, CT
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