Variation and inequality-what are the causes?
Yesterday the NHS Atlas of Variation in Healthcare was launched. It aims to “address variations in activity and spend within the NHS” and “search for un-warranted variation”. Unwarranted variation is defined as “Variation in the utilization of health care services that cannot be explained by variation in patient or patient preferences”, and addressing it may “maximise health outcome and minimise inequalities”. The media coverage, as expected, has focused on the shocking “postcode lottery” of NHS healthcare with a 14-fold difference in hip replacement rates and a three- to four-fold variation in the percentage of patients getting the best possible stroke care. Across countries and across disease areas, there has been a flurry of research to show both VARIATION and INEQUALITIES. What do these words mean?
Variation, variability and statistical dispersion are terms often used interchangeably, but they all describe the spread of a variable. Variation can be described using measures such as the standard deviation, the range and the coefficient of variation (CV). For example, the CV is defined as the ratio of the standard deviation to the mean. CV, unlike the standard deviation or the range, does not have units-ie. It is dimensionless.
Variability can occur due to random measurement errors. For example if we assume the outdoor temperature to be fixed, the variation between measurements is due to observational error. With people, such assumptions are false: observed variation is because distinct members of a population differ greatly. For example, the way we measure blood pressure has been called into question by recent research about blood pressure variability
The Longman’s dictionary defines “inequality” as “an unfair situation, in which some groups in society have more money, opportunities, power etc than others”. So “inequalities” are “unwarranted variation”. Probably the most famous recent studies of health inequalities are Sir Michael Marmot’s Whitehall Studies, first started in 1967, showing that men in the lowest employment grades in the civil service were much more likely to die prematurely than men in the highest grades, and led to the study of “socioeconomic inequalities in health”. The WHO set up a Commission for Social Determinants of Health, led by Marmot, which has published several reports on how to address social health inequalities. Another example of health inequalities research is the Global Burden of Disease project of the WHO has studied variations and inequalities in global disease distribution.
But the difficult part is characterising what causes these variations. The Right Care programme, led by Sir Muir Gray, has for the first time attempted to aggregate what the NHS spends on particular groups of disease. Perhaps surprisingly, this list is topped by more than £10bn spent on mental health in England, £7.5bn on circulatory diseases, and £5bn on cancers. The unpacking of this kind of data is where the real inequalities will get tackled.