204 Chapter 7 METHODOLOGICAL CONSIDERATIONS Measurement challenges are everywhere Even though the terms are often used interchangeably, there are important conceptual differences between inequality and inequity. Equity is a normative concept that applies to inequalities that are unjust or unfair and avoidable [20]. Empirically, this difference is often difficult to measure. In the context of inequalities in health care, for example, assessing the difference between inequalities and inequities depends on the ability to measure the need for treatment. Following from the horizontal equity principle, policy should aim at reducing inequalities in care that are not justified by individuals´ differences in how they need these services. In this thesis, need was approached in two different ways. In Chapter 2, which focuses on patients, we measured need more comprehensively than most research so far: combining disorder diagnosis and patient functioning, as measured by GAF. Despite need measurement being a methodological strength of this paper, our approach has some limitations namely those linked to the subjective nature of the therapist-assessed GAF [21, 22]. Chapter 3 studied access to mental health care looking at the entire youth population in the Netherlands. Although the administrative data used is quite rich, it did not allow quantifying whether each youngster would need treatment or not. In fact, need is harder to account for when studying access to services than utilisation of services. This is because need measures will often be available in clinical contexts for those already in treatment but are less common in data sources covering the entire population. To interpret the findings in Chapter 3 we complemented our primary analysis with a secondary analysis that focused only on youngsters treated in the previous year (i.e. patients). For these patients, we used their previous consumption as a proxy for their treatment (continuation) need. The results showed substantial rates of treatment cessation in patients with prior higher treatment intensity, measured through expenditure, and for patients taking one or more medications for mental health disorders. These findings suggest that at least part of the care foregone by youth patients when facing high deductibles would have been needed. A different but equally important challenge relates to measuring inequalities by socioeconomic status (SES). SES is a “theoretical construct of socioeconomic hierarchies with roots in the social theories of Weber and Marx”, conceptualised through indicators or measures collected at the individual or area-based level [23]. Even though there is usually an intuitive sense of what SES means, the complexity of the SES construct creates several challenges in fully measuring and interpreting the many dimensions it entails, and how they relate to each other [24]. In Chapters 2 and 3 of this thesis we measured equivalised household income as a key determinant of SES. There were several reasons behind this choice, including our hypotheses for the main mechanisms driving the inequalities (e.g. financial barriers in Chapter 3) and the quality and availability of the data. In Chapters 4 and 5, the analysis of patient SES occupies a less relevant part of the studies (the heterogeneity analysis and the adjustment for patient case mix, respectively). Again, the
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