Council tax valuation banding as a surrogate marker of
socioeconomic position in the primary and secondary prevention of coronary heart disease.
MSc(R) thesis, University of Glasgow.
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Coronary Heart Disease (CHD) is the commonest cause of premature death in men and women in Scotland. Research has suggested that a significant proportion of incident CHD is attributable to modifiable risk factors such as level of physical activity, diet and smoking. This recognition that CHD is a largely preventable disease has focused health policy, both in the UK and elsewhere, on prevention strategies.
There is well established evidence of a socioeconomic gradient in CHD; where those of lowest socioeconomic position (SEP) experience the highest CHD burden and greatest exposure to cardiovascular risk factors. This presents distinct challenges for effective primary prevention (defined as the prevention of new-onset CHD) and secondary prevention (defined as the prevention of recurrent coronary events in patients with established CHD) of the disease. A key consideration in the implementation of CHD preventative strategies is thus the measure of SEP used in the allocation of preventative resources.
This study will investigate the predictive validity of Council Tax Valuation Banding (CTVB) in identifying high-risk sub-groups within both CHD primary and secondary prevention populations. CTVB is worthy of consideration as a marker of SEP in this context as it appears to have several appealing characteristics appropriate for use in CHD prevention. CTVB is based on the property value; theoretically reflecting both individual material circumstance and to an extent geographical area characteristics. Furthermore CTVB is objective, uncomplicated, universally available and sensitive to the household level. This study originated from an interest in developing practical and applicable methods of identifying highest risk individuals within CHD prevention populations. Gaps in existing research support a need for this.
Firstly a cohort of just under 2,000 men and women, aged between 45-60 years who participated in the Have a Heart Paisley (HaHP) CHD Primary Prevention Programme was examined. These individuals were enrolled in 2006 and underwent comprehensive cardiovascular risk screening. Secondly, in 2009, the HaHP Chronic Disease Register (CDR) was used to pool Secondary Prevention primary care data for just over 3,000 men and women, of all ages with established CHD.
Socioeconomic patterning of risk factors and absolute risk was examined in the primary prevention population. Socioeconomic inequalities were examined in risk-factor monitoring and therapies prescribing in the secondary prevention population. SEP for analyses in both populations was measured using the Scottish Index of Multiple Deprivation (SIMD) and CTVB- which was supplied by the Renfrewshire Joint Valuation Board. Both measures of SEP were linked to these data using address information and postcodes.
The findings of this study demonstrate some potential for the use of CTVB as a surrogate marker of SEP in health research and cardiovascular preventative strategies. But that further research on this matter is required. CTVB showed significant association with few classical cardiovascular risk factors in the primary prevention population; body mass index in females, high-density lipoproteins (HDL) cholesterol in females, and rates of current smokers in both males and females (age and age-squared adjusted). However all associations with the exception of rates of current smokers (both males and females) became insignificant when SIMD was added into the statistical modelling. CTVB displayed association with Framingham risk scores in both men and women (age and age-squared adjusted) however added independent predictive power in men only.
The associations between SEP (as measured by CTVB) and classical risk factors in the present study are generally weaker than the literature reviewed using established measures of SEP. Particularly striking is the insignificant socioeconomic variance in blood pressure levels when using CTVB, which is at odds with the overwhelming majority of literature in this field to date. Aside from the CTVB analyses, in general the analysis undertaken adds to existing literature; re-enforcing the existence of socioeconomic inequalities in classical risk factors and absolute risk in an asymptomatic population.
When examining the secondary prevention population, significant socioeconomic (using CTVB as a measure of SEP) variance was identified in risk-factor monitoring and in some therapies prescribing. The analyses demonstrates that the removal of “exception reporting” from the Quality Outcomes Framework (QOF) records reveals some important inequalities in care and treatment within an established CHD population. The analyses did demonstrate that overall rates of risk factor monitoring and therapies prescribing have risen markedly over the past decade, especially post introduction of the QOF. These findings have important implications for the delivery of the QOF in Scotland and for Secondary Prevention of CHD in general.
Considerable methodological difficulty was encountered when using CTVB as a surrogate marker of SEP. Data linkage based on address and postcode data proved problematic, notable proportions within each population required matching “by hand” which proved time consuming. Furthermore use of CTVB in this study identified significant potential to misclassify the SEP of individuals who are renting properties; particularly homes of multiple occupation. Additionally the marked rise in housing price over the past two decades in the UK may further compromise CTVB’s accuracy as a measure of SEP.
Such practical and theoretical limitations of the use of CTVB as a marker of SEP have not been reported in the literature to date. This supports the conclusions of the literature review within the present study which question the quality and scientific objectivity of studies examining CTVB as a marker of SEP undertaken thus far.
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