Disease prevalence models: CHD, hypertension, stroke and COPD
As part of the 2007/8 Local Delivery Plan (LDP) process the Association of Public Health Observatories (APHO) was commissioned by the Department of Health to produce PCT level prevalence estimates for hypertension and coronary heart disease. However, it was acknowledged that the initial versions were rather crude and APHO subsequently commissioned Michael Soljak of the Department of Primary Care and Social Medicine, Imperial College, London to develop more robust models for COPD, CHD, hypertension and stroke.
These new models are based on multinomial logistic regression of data from the Health Survey for England. The models have then been applied to population data at PCT and LA level.
Hypertension
This supersedes the model developed by the Faculty of Public Health and the Yorkshire and Humber Public Health Observatory and previously published by APHO. The model includes sex, age, ethnicity and deprivation.
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CHD
This is based on HSE data using a definition of CHD of self-reported doctor diagnosed CHD which has been shown to be predictive of objective CHD adjusted for PCT level deprivation. The new model is more sophisicated than the crude model previously published by APHO to support the 2007/8 LDP process. The model includes sex, age, ethnicity, smoking status and deprivation.
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Stroke
Based on HSE data from 2003-2004, this model includes age, sex, smoking status and deprivation.
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COPD
The model is based on CHD data and includes sex, age, ethnicity, smoking status, rurality and deprivation. The estimates were updated in October 2008 to use the latest available input data.
The classification of areas as urban, suburban or rural is difficult and can have a significant impact on the modelling results, particularly for areas that could be classified as urban or rural. An algorithm for classification of PCTs and LAs was developed, based on the DEFRA categories and APHO urban-rural definition. This algorithm results in the same distribution of urban, suburban and rural local authorities as seen in HSE 2001. However, some areas that are classified by DEFRA as Major Urban or Large Urban end up in the suburban category in the model, which is arguably a mis-classification. Alternative modelling results have been calculated for these areas (14 PCTs and 26 LAs) using an urban instead of suburban, classification.
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