160 Chapter 5 (2.9%). A flow diagram describing the selection of the study population is presented in the supplement (Figure A1). Variables The outcome variable is GP antidepressant prescription share, among patients identified with depression in GP´s patient list. This share was calculated for each year by dividing the total number of adults (18 years and older) identified by the GP with a diagnosis of depression and who were prescribed antidepressant therapy, by the total number of adults identified by the GP with a diagnosis of depression. All major classes of antidepressants alone or in combination were considered (group 2.9.3 of the national pharmacotherapeutic classification of drugs4, equivalent to group N06A from the Anatomical Therapeutic Chemical Classification System). GPs diagnosis of depression followed the International Classification of Primary Care 2 (ICPC-2) and included affective psychosis, depressive neurosis, depressive psychosis, mixed anxiety and depression, reactive depression, and postnatal or puerperal depression (P76). Data on our outcome variable - from now onwards often referred to as antidepressants prescription - is usually collected in primary care to monitor the prescription behaviour. Importantly, this indicator is not used to measure GPs performance or to apply incentives, because it does not allow conclusions to be drawn about the appropriateness of antidepressant use. Our exposure variable of interest is the supply of psychological therapy services by psychologists. It was computed for each year as the number of psychologists in fulltime equivalents (FTE) per 100,000 patients enrolled in the local group. Primary care psychology teams are multidisciplinary and can include specialised nurses, occupational therapists, and social workers. We excluded other professionals than psychologists from our explanatory variable because, in Portuguese primary care, they do not provide psychological therapy interventions. Furthermore, a comprehensive set of GP and GP practice covariates were included in our models, informed by literature and the Portuguese context. Physician characteristics included are age in years, sex (female or male), tenure in the GP practice (1 to 2, 3 to 5, or more than 5 years), patient list size and the utilization share (share of patients with at least one yearly visit). Other covariates accounting for the patients’ list characteristics measured its demography (proportion of female patients and patients in each age group) and morbidity (prevalence of dementia, chronic obstructive pulmonary disease, cancer, asthma, hypertension, obesity and diabetes). Practice-level covariates controlled for the practice organizational model (personalised health care units – PHCU; family health units type A and B - FHU-A and FHU-B), the number of years the practice had been operating in the current arrangement, the share of patients enrolled in the practice but not listed 4 Ministry of health order nr 2977/2014 Available online: https://dre.pt/dre/detalhe/despacho/4742-2014-25681511 (accessed on Jan 2023).
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