Researchers claim clinical trials are reported with misleading statistics
BMJ 2002; 324 doi: https://doi.org/10.1136/bmj.324.7350.1353/a (Published 08 June 2002) Cite this as: BMJ 2002;324:1353
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Prevention is better than cure, but the effect of
most preventive measures is trivial. The
relative risk reduction is therefore highly misleading, as pointed out by Nuovo et al.
(1), but even the absolute risk reduction, or number needed to treat, means almost nothing
to most patients.. For this group it is much more ‘honest’ and effective to
provide the figures that represent their chances of surviving with and without treatment.
To give an impression of
the small improvement that is achieved by commonly used preventive measures I have
calculated the chance of surviving with and without treatment of hypertension, and with
and without treatment of hypercholesterolaemia (table).
For hypertension I have used the figures from a meta-analysis of seventeen
controlled, randomised trials (2). For hypercholesterolaemia I have used the data from the
4S (3) , as it demonstrated the most favourable outcomes in patients with established
cardiovascular disease, and the data from the WOSCOPS trial (4) as this trial demonstrated
the most favourable outcome in healthy individuals with high cholesterol. In both trials I
have chosen the figures for total mortality, because I assume that this is the most
relevant figure for most patients, and because no bias is associated with that outcome.
For the hypertension trials total cardiovascular mortality is the measurement used,
because a meta-analytic calculation of total mortality was not performed.
| Table. Benefits from treatment of high blood pressure and of high cholesterol |
BP lowering |
4S | WOSCOPS |
| Relative risk reduction; % | -20 | -29 | -21 |
| Absolute risk reduction; % | -0.8 | -3.3 | -0.9 |
| Chance of surviving without treatment; % | 96 | 88.5 | 90.6 |
| Chance of surviving with treatment; % | 96.8 | 91.8 | 91.4 |
As mentioned, these figures are the most optimistic available. For instance,
in many of the studies that were included in the meta-analysis on hypertension, total
mortality was not reduced significantly. Further, the results from the most recent
secondary preventive statin trial HPS were only half as good as those from 4S (5); and
total mortality in the first primary preventive statin trial EXCEL was increased in the
treatment group (6). If patients were given these odds, and then clearly informed about
possible side effects from treatment, I guess that most of them might choose to spend
their money on horse racing.
- Nuovo J, Melnikow J, Chang D. Reporting Number Needed to Treat and Absolute
Risk Reduction in Randomized Controlled Trials. JAMA
2002;287:2813-4 - Hebert PR, Moser, M, Mayer J, Hennekens CH. Recent evidence on drug therapy of mild to moderate hypertension an decreased
risk of coronary heart disease. Arch Int Med
1993;153:578-81. - Randomised trial of cholesterol lowering in 4444 patients with coronary heart
disease: the Scandinavian Simvastatin Survival Study (4S) Lancet 1994;344:1383-9. - Shepherd J, Cobbe SM, Ford I, Isles CG, Lorimer AR, Macfarlane PW, McKillop
JH, Packard CJ, for the West of Scotland Coronary Prevention Study Group. Prevention of
coronary heart disease with pravastatine in men with hypercholesterolemia. N Engl J Med 1987;333:1301-7. - Ravnskov U. Statins as the new
Aspirin. Conclusions from the heart protection study were premature. BMJ
2002;324:789. - Bradford RH, Shear CL, Chremos AN, Dujovne C, Downton M, Franklin FA, Gould
AL, Hesney M, Higgins J, Hurley DP, et al. Expanded Clinical Evaluation of Lovastatin
(EXCEL) study results. I. Efficacy in modifying plasma lipoproteins and adverse event
profile in 8245 patients with moderate hypercholesterolemia. Arch Intern Med
1991;151:43-9.
Competing interests: No competing interests
I have always thought that doctors are continually subjected to pressure from the
pharmaceutical industry and what a pressure. I used to be a
researcher and depending how your data are shown you can show whatever you
intend to.
So caution and chicken soup is always clever whenever dealing with an
endless number of new wonder drugs.
Statistical background is fundamental when analysing any medical article
and unfortunately not everybody has it to the proper extent.
So I cannot feel free of a feeling of being trapped in the
pharmaceutical net.
Competing interests: No competing interests
Re: Chance of surviving with and without treatment
I guess it would be even more "honest" if time is involved in
discussions with patients. Will the pill delay death and for how long?
Survival is a relative term within the human condition.
Competing interests: No competing interests