29 Income inequalities beyond access to mental health care Outcomes We assessed four outcomes corresponding to different mental health treatment stages. First, we measured income disparities in disease severity at baseline using the GAF scores rated by a mental health professional at record opening. The GAF consists of a 100-point scale divided into ten-point interval categories. These range from indicating “persistent danger of severely hurting self or others (e.g. recurrent violence), persistent inability to maintain minimal personal hygiene, or serious suicidal acts with clear expectation of death” for 1–10 to “superior functioning in a wide range of activities, life’s problems never seem to get out of hand, is sought out by others because of his or her many positive qualities. No symptoms” for 91–100 [25]. In the treatment records data, mental health professionals selected one of the ten interval categories to rate disease severity (Table A3). Second, we investigated income disparities in the number of treatment minutes. Treatment minutes were calculated as the sum of direct treatment minutes spent by mental health professionals with the patient in both inpatient and outpatient settings, either individually or in group therapy, and indirect treatment minutes, spent on treatment activities in the absence of the patient, such as administrative or preparatory tasks. In the statistical analyses we used the natural logarithm of treatment minutes to diminish the influence of outlying patients with high treatment minutes (Figure A2.) and to allow us to interpret effect sizes in terms of percentages [26]. Third, we documented income disparities in functional improvement by the end of the first observed treatment record. We defined functional improvement as a binary outcome, indicating whether the GAF category at the end of the record was higher than the initial GAF category. Finally, we examined income differences in the probability of having an additional treatment record. This outcome was a binary indicator of whether a subsequent treatment record was opened within 90 days after the closure of the initial record. The subsequent record could be opened for various reasons, such as continuation of care, treatment needed after a relapse or recurrence, or changes in provider driven by new diagnoses or needs or because of patient preferences. Exposures and covariates Net equivalised household income was measured as the household income net of taxes and social security contributions in the year of treatment initiation [27], adjusted for household size using the Statistics Netherlands equivalence factor [28]. Patients were then assigned to one of five income quintiles on the basis of the net equivalised household income distribution of the Dutch adult population in the same year. Our main analyses controlled for the month and year in which the treatment record began, to account for seasonality and annual policy changes; age in years at treatment initiation; a binary indicator for gender; a categorical variable characterising migration 2
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