As a patient subject to the guidelines in practice one begins to wonder at the “targets” so defined for various parameters. Taking the statement in the editorial:
“Use of the more intensive target led to a statistically significant but modest difference of about 3 mm Hg in SBP between groups”
one wonders at precisely what a change of 3 mm Hg actually accomplishes both in terms of “risk” and in terms of adverse reactions in individual patients. What in fact is the increased drop out rate actually responding to? It apparently of no concern to the medical statisticians.
Furthermore, a paper by Port (Lancet. 2000 Jan 15;355(9199):175-80) has shown that, to quote:
“The Framingham data contradict the concept that lower pressures imply lower risk and the idea that 140 mm Hg is a useful cut-off value for hypertension for all adults. There is an age-dependent and sex-dependent threshold for hypertension. A substantial proportion of the population who would currently be thought to be at increased risk are, therefore, at no increased risk.”
a point that has been studiously ignored by those who support the paradigm of a linear response between SBP and risk of CHD and/or stroke.
Another interesting quote from a comment to the Lancet (2000) is:
It is a curious fact that simply fitting a statistical model to data can give the impression that the assumptions of the model are supported by the data. Sidney Port and colleagues reassess the Framingham data, in which a linear-logistic model has previously been used to relate all-cause mortality to systolic blood pressure: this model assumes that the odds ratio for death for a 10 mmHg increase in systolic blood pressure is the same at all levels of systolic blood pressure. Port and colleagues show convincingly that this assumption is false, and they propose a better model in which the odds ratio for a 10 mmHg increase in systolic blood pressure is larger at systolic blood pressures above the 70th centile.
While I am a keen supporter of statistics (my interest goes back to 1953), these days I get the impression that they takes precedence over all; odds ratios are prime but unfortunately as a ratio of two ratios, which, while helping to demonstrate significance they also conceal the real numbers and benefits and non-benefits. What seems always to be forgotten is the patient and the probability that he or she will benefit (or not benefit as the case may be) from the therapy. Unfortunately, in many cases these days, while therapies may be statistically beneficial, the actual benefit may be trivial and improbable.
Rapid Response:
Re: Blood pressure targets in primary care
As a patient subject to the guidelines in practice one begins to wonder at the “targets” so defined for various parameters. Taking the statement in the editorial:
“Use of the more intensive target led to a statistically significant but modest difference of about 3 mm Hg in SBP between groups”
one wonders at precisely what a change of 3 mm Hg actually accomplishes both in terms of “risk” and in terms of adverse reactions in individual patients. What in fact is the increased drop out rate actually responding to? It apparently of no concern to the medical statisticians.
Furthermore, a paper by Port (Lancet. 2000 Jan 15;355(9199):175-80) has shown that, to quote:
“The Framingham data contradict the concept that lower pressures imply lower risk and the idea that 140 mm Hg is a useful cut-off value for hypertension for all adults. There is an age-dependent and sex-dependent threshold for hypertension. A substantial proportion of the population who would currently be thought to be at increased risk are, therefore, at no increased risk.”
a point that has been studiously ignored by those who support the paradigm of a linear response between SBP and risk of CHD and/or stroke.
Another interesting quote from a comment to the Lancet (2000) is:
It is a curious fact that simply fitting a statistical model to data can give the impression that the assumptions of the model are supported by the data. Sidney Port and colleagues reassess the Framingham data, in which a linear-logistic model has previously been used to relate all-cause mortality to systolic blood pressure: this model assumes that the odds ratio for death for a 10 mmHg increase in systolic blood pressure is the same at all levels of systolic blood pressure. Port and colleagues show convincingly that this assumption is false, and they propose a better model in which the odds ratio for a 10 mmHg increase in systolic blood pressure is larger at systolic blood pressures above the 70th centile.
While I am a keen supporter of statistics (my interest goes back to 1953), these days I get the impression that they takes precedence over all; odds ratios are prime but unfortunately as a ratio of two ratios, which, while helping to demonstrate significance they also conceal the real numbers and benefits and non-benefits. What seems always to be forgotten is the patient and the probability that he or she will benefit (or not benefit as the case may be) from the therapy. Unfortunately, in many cases these days, while therapies may be statistically beneficial, the actual benefit may be trivial and improbable.
Competing interests: No competing interests