odes, or recurrent episodes provided there was a year between episodes. There is limited comparable incidence data from other sources, as most data pertain to prevalence28 or are based on epidemiological studies using diagnostic case finding in the community or with screened practice attendees, rather than GP identification and recording.
Our study found an overall combined incident rate of recorded depression (diagnoses and symptoms) of 2.5%. This is lower than incidences found in epidemiological studies, which use case-finding and are limited to major depressive disorder. For example, in the PREDICT study in six European countries,29 the 12-month cumulative incidence of DSM–IV major depression in screened GP attendees was 7.7%, and in the UK was 8.8%. A systematic review in 2004 of international incidence studies of mood disorders16 identified four community studies but no primary care studies. They calculated a best-estimate rate for 1-year community incidence of major depressive disorder of 2.9 per 100 PYAR. The World Health Organization study in 15 international centres30 found 4.4% with new diagnoses of ICD–10 depressive episodes. In one of the studies closest to ours in design, a retrospective USA cohort study31 conducted in 39 practices in 1996 looked at incidence of first-ever recorded depressive episode in primary care settings in electronic records, excluding people with any history of depression or its treatment. They found that 2103 (1.6%) of the 131 141 eligible patients had a first-ever episode of recorded depression over 1 year. Our study was not limited to first-ever episodes. There is evidence that GPs may not record depression that they recognise. In a two-phase observational GP study based in seven practices,32 which looked at GP identification and prescribing for depression, GPs discussed depression with about half of the patients that they considered to have depression.
Strengths and limitations
This is one of very few studies examining the incidence of recorded depression in a large cohort of people seen in primary care. It included data from over 200 000 new episodes of diagnosed depression and over 150 000 new episodes of depressive symptoms recorded in routine primary care settings. A 10-year period was examined and changes over time evaluated. We defined our episodes by problem codes (diagnosis/symptoms) as we were looking specifically at GP-recorded depression. People who received a prescription for an antidepressant without a depression code being entered were excluded, as it was unclear what the GP’s working diagnosis was in such cases. This group would include those prescribed antidepressants for another indication, such as chronic pain, as well as unlabelled depression.
The data are limited to GP-recorded depression in practice attendees, which reflects incidence, presentation and recording at a practice level only. Our data do not include people with whom depression was discussed, but not entered as a problem onto their clinical record. It is therefore very likely that this is an underestimate of GP-recognised depression. There is also little indication of severity from the Read codes used. Most codes entered were non-specific, not allowing for differentiation of subtypes. There is a lack of validation work on depression and depressive symptoms recording in UK primary care databases, and we did not therefore have a gold-standard comparison. There is evidence that non-psychiatric physicians’ recognition of depression has a low sensitivity but high specificity for ‘true’ cases measured using standardised instruments.14 As computers are used more in practice, GPs are coding more problems, but also using the non-coded free text options more. These comments may allude to recognised depression, but will not get picked up in a search, resulting in an underestimate of the incidence.
This study suggests that the way that GPs choose to record depression has changed over the past decade. General-practitioner recording of depression diagnoses is lower than that reported in studies on GP attendees usi