Saturday, March 5, 2011

Antidepressant prescribing in England: variation may not be as great as Guardian map suggests.

The Guardian published a story on March 5th, 2011, showing that the crude rate of anti-depressant prescribing in some areas of England was more than 3 times higher than in others.The highest rate of prescriptions was in Blackpool, and the lowest in Kensington and Chelsea.
The data was from publicly available sources and is linked to from the Guardian website. The journalists give this description of their method :
"How did we arrive at our figures? First, we gathered prescription data from the online database managed by the NHS Information Centre.

This quarterly information was compiled to get annual numbers covering 1 April 2009 to 31 March 2010 – the most recent full year with available data. In order to make the numbers comparable, we then linked the raw prescription numbers to the ONS mid-year population estimates.
This allowed us to calculate the prescriptions per 100,000 figure in the data below, which controls for the different sizes of PCTs, if not their different levels of wealth, employment and general illness."

The data is also not age standardised. In the comments section some have suggested that in areas with low numbers of prescriptions doctors may be prescribing several months prescriptions at one time. I have looked at the most recent data set available (July-August 2010). Data is available on the total cost of the prescriptions as well as the number of prescriptions and these are plotted below.

This shows a clear correlation between number of prescriptions and cost. However when one looks at individual PCTs the average cost of an antidepressant prescription in Kensington and Chelsea PCT is £7.01, whilst in Blackpool PCT it is £3.48. This does suggest that either more expensive antidepressants are being prescribed in Kensington and Chelsea, or more months prescriptions are being given at one time. Since the absolute number of prescriptions in Kensington and Chelsea is so much lower than in Blackpool, it may be that more antidepressants are being prescribed in each prescription. 

When looking at datasets it's good to make use of all that is available.

You can find my spreadsheet here.

EDIT 4.20pm 6/3/11 I've calculated a rate of prescribing of antidepressants per 1000 of population over 19. (This is not ideal as some teenagers may be prescribed antidepressants, but more accurate than using the total population including children). This has been plotted against average cost of antidepressant prescription. This shows that Blackpool and Kensington and Chelsea are outliers. 

There is not a strong relationship between cost of prescriptions and number of prescriptions. This may explain some of the variation between north and south of England, but the long-established relationships between deprivation and depression are likely to have greater explanatory power.

Here is a link to some papers on that relationship and a very interesting report (via @coxar) on the relationship between antidepressant prescribing, poisoning by antidepressants and deprivation.

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