al practitioners’ coding may be linked to the perceived severity of depression, with symptom codes being used for milder depression. It may also be explained by greater questioning of the meaning of psychiatric diagnostic categories in primary care23 and a move away from the use of discrete categories that have dominated psychiatric research and practice. General practitioners may be increasingly unhappy to label people with distress and low mood as having ‘depressive disorder’, and with the increased use of computer coding for consultations have started to enter symptom codes instead. General practitioners have a relationship with their patients that often results in diagnosis being made in a longitudinal manner.24 General practitioners take into account many psychosocial variables, but are also influenced by their own attitudes and the consulting environment, particularly time issues.25,26 Diagnostic validity remains a challenge. There is a continuing debate around whether GPs underdiagnose depression, when compared with psychiatric instruments, or whether they are recognising ‘true’ depression, and not medicalising normal human distress.11,23
The relationships between recorded depression diagnoses and symptoms, and gender and deprivation observed in this study are consistent with epidemiological research.27 The highest incidence rates in our study were in the 25- to 44-year-old age group for women and in the 44- to 65-year-old age group for men. This compares with contemporary studies of GP populations where the highest prevalence of depression was in women aged 18 to 30, and men aged 30 to 50 years.8 Over the study period the relative incidence of depression diagnoses has remained twice as high in more deprived areas compared with least deprived areas. This inequality is marked and stable over time. The same findings were observed with regard to depressive symptoms.
Comparison with other studies
Our study looked at the incidence of recorded depression diagnosis or symptoms. We included people with single episodes, 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 