d as an everyday problem of practice, rather than an objective diagnostic category.11 Standardised diagnostic interviews are not used in primary care to diagnose depression, and it is known that more severe depression is more likely to be recognised in primary care settings.12,13 A recent meta-analysis14 found that non-psychiatric physicians’ recognition of depression had a low sensitivity (36.4%) but high specificity (83.7%) for ‘true’ cases measured using standardised diagnostic instruments; however, non-psychiatric physicians may deliberately avoid labelling people with mild symptoms as being depressed. Therefore, categorical approaches to diagnosis have been questioned in favour of a multidimensional approach,15 which may be more relevant to primary care.12
Epidemiological surveys have shown that depression diagnoses are higher in women, older people and those living in deprived areas. We do not know whether this is mirrored in the rates of general-practitioner (GP) recording of depression diagnoses and depressive symptoms. There are few data on depression incidence in primary care and primary care recording of depression, in contrast to the wealth of epidemiological data on prevalence.16 We examined a large UK primary care database to determine the incidence rates of recorded depression diagnoses and depressive symptoms in attenders from 1996 to 2006. We also determined whether there were differences in incidence of recording of diagnoses or symptoms by sociodemographic factors. The study was given a favourable opinion by the London Medical Research Ethics Committee (07/MRE02/5).
We used data from 298 UK general practices, providing two or more years of data to The Health Improvement Network (THIN) from January 1996 to March 2006. We only used practices meeting standards for acceptable levels of data recording. The total registered patient population during this time period was 4 986 111 people, comprising 21.6 million years of follow-up.
The Health Improvement Network (THIN) electronic recording scheme is one of the largest UK sources of continuous primary care data on illness recording and prescribing behaviour (http://www.thin-uk.com/). It has been used for epidemiological studies,17,18 including work on antidepressants and suicide.19 Anonymised patient data are pre-collected from participating practices. Practices are broadly representative of UK general practices in terms of patients’ age and gender, practice size and geographical distribution.20 General practitioners enter medical diagnoses and symptoms using Read codes. Read codes are a hierarchical recording system used to record clinical summary information. The codes are not limited to diagnostic and procedural codes, but also include codes for symptoms, test results, screening and other areas. The age, gender, medical diagnosis and symptom records, health promotion activity, secondary care referrals, prescriptions and quintiles of deprivation score are recorded for each registered individual.
All adults aged 16 years and over registered with practices providing acceptable levels of recording during the study period (1996–2006) were included in the study. All participants had a minimum of 1-year follow-up data.
Read code lists were developed by the study team (Online supplements 1 and 2) to identify either recorded diagnoses of depression (e.g. ‘depressive disorder’) or recorded depressive symptoms (e.g. ‘low mood’). A new episode of diagnosed depression was defined as an entry in the records where there was no previous diagnosis of depression coded in the previous year. A new episode of depressive symptoms was also defined as an entry where there had been no previous recorded depressive symptom code in the previous year. Participants could have more than one new episode within the study follow-up period, providing there were 12 months between episodes.
We excluded data from the first 12 months following registration with their GP, as this may be retrospective recording of a past history rather than a true incident recording of a new episode of depression.