Morbidity statistics are much harder to collect than mortality statistics. Sources of morbidity data include routinely collected national data, national studies and local studies. Each source has its pros and cons. Most sources only provide data on one or two aspects of morbidity from CHD and related conditions. Not all sources supply data for all ages or even both sexes. Data are collected in different ways with different degrees of validity and reliability. Sample sizes vary considerably as do sampling methods.

In compiling the morbidity section of the heartstats website we have aimed to investigate and cite all possible sources of recent data relating to morbidity from CHD and heart failure in the UK but have presented data, and calculated UK estimates, only from studies which give the widest coverage in terms of age, sex, geographical location, etc. and also which used valid and reliable methods of data collection.

We have not included data from studies carried out outside of the UK (except when making international comparisons).   There are however various non-UK sources of data which might provide useful indicators to the likely situation in the UK for example studies in Framingham (US), Gothenburg (Sweden), Reykavic (Iceland) etc.   We have not included data from studies carried out prior to 1985 (except for time-trend data).   

Data from trials of drugs or surgery, have not been included either, because the subjects of such trials are generally only a selected proportion of the population.   We have included baseline data from one trial of different implementation strategies for promoting secondary prevention of CHD in general practice - the ASSIST trial – because this study did not involve selection of particular patients.