were non-specific codes: ‘ depressive disorder NEC’ (not elsewhere classified) (n = 90 928 episodes, 35.6%) and ‘depression NOS’ (not otherwise specified) (n = 46 681 episodes, 18.2%). The most common symptom codes were ‘depressed’ (n = 46 071, 29.4%) and ‘ complaining of feeling depressed’ (n = 45 203, 28.8%).
Owing to the large sample size (events and PYAR) all associations were found to be statistically highly significant (P<0.0001). The magnitude of the IRRs and associated 95% confidence intervals (CIs) were therefore of primary interest in interpreting any associations.
Incidence of recorded depression diagnoses
The incidence of recorded diagnoses fell from 22.5/1000 PYAR in 1996 to 14.0/1000 PYAR in 2006 (IRR = 0.64, 95% CI 0.57–0.71; online Table DS1). Females were more than twice as likely to have a diagnosis recorded than males. People in the 25 to 44 age group had the highest rate of diagnosed depression, their incidence being more than 50% higher than those in the 16 to 24 age group. People in the most deprived group had nearly twice the rate of depression diagnosis compared with the least deprived group. The effect of gender and deprivation on incidence of depression did not change substantially with time (online Table DS1).
There was an interaction of age with calendar year, and age with gender. Therefore the IRRs for year, compared with the baseline of 1996, were stratified by both age and gender (Tables 1 and 2). The incidence of recorded depression over time fell more markedly in older (aged 65 years or more) compared with younger age groups. For example, in 1996 the incidence of diagnosed depression in those aged 75 and over was 32% greater than that for 16- to 24-year-olds. By 2006 this was reversed with the incidence in those aged 75 and over being 23% lower. In females the overall incidence of depression in those aged 75 and over was 16% less than in the 16- to 24-year-olds, whereas in males there was a 43% increase.
Incidence of recorded depressive symptoms
The incidence of recorded depressive symptoms rose threefold from the baseline of 5.11/1000 PYAR in 1996 to 15.5/1000 PYAR in 2006 (online Table DS2). Females had symptoms recorded twice as often as males, which is similar to the findings of recorded diagnoses. Adults in the 25 to 44 age group had the highest rate of depression symptoms, compared with those in the 16 to 24 age group. Those in the most deprived group had depressive symptoms recorded nearly twice as often as the least deprived group.
For recorded depressive symptoms there was an interaction of age with calendar year and age with gender, so the IRRs for year, compared with the baseline of 1996, were stratified by age and gender (Tables 1 and 2). In 1996 the incidence of depressive symptoms in those aged 75 and over was 41% greater than in the 16- to 24-year-olds, whereas in 2006 the incidence was 32% less. There was a lower incidence of recorded depressive symptoms in older age groups (aged 65 years or more) compared with younger age groups in women, but this difference was less marked among men. The effect of gender and deprivation on incidence of symptoms did not change substantially with time.
Combined incidence for diagnoses and symptoms
The results above demonstrate a fall in the recorded incidence of diagnosed depression, but an increase in recorded depressive symptoms, although the combined incidence rates varied little over time (Fig. 1). The combined incidence over the study period was 24.8/1000 PYAR, equivalent to a mean annual incidence of 2.5%. We had categorised depression codes into two lists (diagnoses and symptoms) and included the code ‘depressed’ in the symptoms list. However, this code is commonly used and may be used by GPs as a diagnostic code, so we re-analysed the data with ‘depressed’ as a diagnostic code. This made only a small difference, slightly increasing the incidence of diagnosis, and decreasing the incidence of symptoms, and made no appreciable difference to the IRRs.
Since 1996 the incidence of recorded diagnoses of depression in UK general practice h