Measuring Prevalence

One of the questions often asked by GPs about QOF data is what their prevalence data should be. There are three ways to measure the prevalence of a condition. First you can ask doctors, second ask patients and thirdly you can get out there and thoroughly examine a random group of people.

The data from QOF on this site is definitely in the first camp. I have come across some interesting disease prevalence models which try to compare QOF data against data from the Health Survey for England which is largely, as the name suggests a survey of the asking patients variety. It does however features some objective measurement by nurses as well.

There is only analysis for heart disease and hypertension. In heart disease there is a small reduction in prevalence in QOF compared to the HSE estimation. This is probably down to a lack of coding. The differences in hypertension prevalence are much larger with the HSE prevalence over double the QOF prevalence.

Now I have to admit that I boggled at this for a while. Could it really be that a quarter of all my patients had hypertension? Well the answer by strict interpretation seems to be "Yes". In fact the data, including the difference between the diagnosed and the actively treated has been observed for some time.

Now I don't propose to go through the rights and wrongs of this but the fact remains that prevalence varies widely possibly predictably depending who you ask. We don't have the official figures for this year's prevalence but kidney disease seems certain to come in well under expectations.

So before making comparisons make sure that data is all coming from the same sources. We await the official figures (traditionally Wales has been early with them but not this year).