About the Data

GP prescribing data are aggregated as a monthly total of the number of prescriptions and amount of each drug prescribed by each GP and filled by a patient during the reporting period.

Northern Ireland prescribing data are published by HSC Business Services Organisation. The data are released quarterly, beginning with prescriptions filled April 2013.

English prescribing data are published by the Health & Social Care Information Centre.

Welsh prescribing data are published by Primary Care Services, part of NHS Wales Shared Services Partnership.

Scotland does not release prescribing data at the level of individual GPs. Without these data, there is no way to make comparisons with other UK countries that do. Scotland was excluded from the analysis.

The Detail used complete data for Northern Ireland, England and Wales for the period beginning April 2013 and ending September 2013. All data, except where explicitly stated, pertain to that period.

The World Health Organisation's (WHO) Defined Daily Dose system was used to make drugs comparable across different strengths and dosages.

WHO's daily doses are calculated for drugs according to the Anatomical Therapeutic Chemical (ATC) classification system, which groups drugs according to their active chemical, the organ or system in the body on which they act and their therapeutic, pharmacological and chemical properties.

Drugs in GP prescribing data, however, are specified by British National Formulary (BNF) code, a reference system specific to the UK.

The Detail mapped ATC to BNF codes in order to apply correct daily doses to drugs in the prescribing data. A full record of that mapping is available here.

Drugs were selected for inclusion in the analysis by their ATC classification, corresponding to general pharmacological categories of antidepressants, anti-anxiety drugs, opioid painkillers and benzodiazepine sedatives.

There were 456 individual medications selected for study, comprised of 54 different active chemicals.

In total, data were analysed for 352 GPs in Northern Ireland; 9,563 English GPs and 541 Welsh GPs.

During the study period (April - September 2013), there were 400 million prescriptions recorded in the data, UK-wide, with over 23,000 medications represented in that total.

Filtering the data for the specific drugs in the study, there were over 36 million prescriptions filled UK-wide. Over 3.5 million of those were prescribed by GPs in Northern Ireland.

Notes to Statistics

One major goal of the analysis was to determine how strong were the relationships between local economic circumstance, the prevalence of clinical depression and antidepressant prescription rate.

Geek-Speak Ahead

GP Deprivation Groups

First some gauge of local economics had to be assessed at the level of individual GPs. Official statistical indexes of deprivation at the smallest geographic census level were used.

The above charts show the distribution of GPs in each of four deprivation groups in Northern Ireland, England and Wales. The deprivation groups range from least deprived to most deprived and were calculated by taking the Z-score — a statistical measure that allows for comparison of the scores between countries — for each GP’s local deprivation level.

In Northern Ireland and Wales, The Detail assigned deprivation scores to each GP based on the scores for income and employment levels in the area of each GP’s postcode.

In Northern Ireland, scores were also approximated as an average of deprivation scores within a certain radius of each GP. At several distance intervals (ranging .25 to 5 miles), the distribution of registered patients within each deprivation category was compared to that of the general population, known via the census. It was determined that assessing deprivation scores only in the immediate area of a GP’s location produced the distribution closest to the census distribution. Of course, every GP’s clients will represent a range of economic and social circumstances.

In England, GP profiles include deprivation scores to reflect their patient populations. These were used.

Break points for the overall deprivation groups were determined by averaging the quartiles for the three countries.

The distribution shows that a greater proportion of English GPs lie in areas that would be considered least deprived, compared to Northern Ireland and Wales. To better account for that difference, the analysis compares prescription rates of each country’s GPs within their respective deprivation group.

Deprivation Influence

The Detail tested the correlation between GPs' local deprivation score and antidepressant prescription rate.

The Pearson correlation coefficients for GP deprivation scores and daily doses prescribed per registered patient were .44 for Northern Ireland; .31, Wales; .22, England, all of which were significant at p < .001 .

A few influential outliers were identified via Cook’s Distance for both Northern Ireland and England. Excluding four outlying data points did not significantly improve the correlation coefficient for England. Northern Ireland’s coefficient improved to .48 after excluding two influential outliers.

The differences between correlation coefficients were tested for statistical significance using the Fisher transformation. Northern Ireland’s correlation coefficient was significantly greater than Wales’ and England’s at p < .05 and p < .001, respectively.

Due to low correlation coefficients, antidepressant prescription rates were said to not necessarily be largely affected by economic deprivation levels.

The Detail also tested for correlations with GPs' rate of depression prevalence, reported as part of the Quality and Outcomes Framework. Surprisingly, no significant correlation was found between the prevalence of depression reported by GPs and the rate at which they prescribe antidepressants.

In England, the correlation was significantly stronger than in Northern Ireland and Wales.

No signficant correlation was found between depression prevalence and local economic deprivation scores.

The following chart sets show the results of those analyses:

PLEASE ... don't make health care decisions based on this report alone. We're not doctors. The data presented here are for the purpose of broad consideration. Information on particular drugs should not be considered exhaustive or necessarily applicable to your individual health.