Stephanie Chan wrote:
> I am giving a talk to my housestaff tomorrow on the pitfalls of
> subgroup analysis. Although I could find many examples of flawed
> subgroup analysis, I would like to give a good example of a subgroup
> analysis that showed benefit in a subgroup, while there was no
> benefit in the overall population, and this subgroup analysis was
> subsequently verified by other studies. Does anyone have a good
> example I could use?
Sorry I did not respond in time, but I mention a subgroup analysis done
correctly as the motivating example in Chapter 4 of my book, Statistical
Evidence (www.pmean.com/Evidence.html).
> There has been a lot of published research that shows that heart
> disease is different and more deadly among black patients. Some
> possible explanations of these differences involve the
> renin-angiotensin system in bioavailability of nitric oxide. In a
> study that seemed to show no overall differences in efficacy for a
> drug treatment, hydralazine plus isosorbide dinitrate, for treating
> congestive heart failure, there was nevertheless the suggestion that
> this treatment might be effective when analysis was restricted to
> just the black patients in the study. This study, however, was not
> designed to look for racespecific effects, so the results had to be
> treated as preliminary. The authors of one review state that
> ‘prospective trials involving large numbers of black patients are
> needed to further clarify their response to therapy’ (Carson 1999).
> With this justification, a new randomized trial, recruiting just
> black patients, was begun. This study did indeed show that the two
> drugs were effective among these black patients (Taylor 2004), and
> became one of the first examples of a therapy recommended solely for
> a specific racial subgroup.
>
> The concept of using race or ethnicity in medical decisions is
> controversial, because of the potential for misuse and abuse of this
> information (Bhopal 1997). There is also debate about whether there is
> enough genetic variations among different racial and ethnic groups to
> justify treating them as distinct group. The authors of the second study
> skirt this issue by using the phrase ‘patients who self-identify as black’.
>
> The important lesson, though, is that no study should be examined in
> isolation. You should always be looking for corroborating evidence. The
> subgroup finding (Carson 1999) was indeed a weak form of evidence, but
> it was supported by several mechanistic explanations described above.
> When these results were replicated in an independent study, the evidence
> in favor of this controversial treatment became overwhelmingly persuasive.
I hope this helps.
--
Steve Simon, Standard Disclaimer.
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