Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Hence, with the understanding that measuring instruments need to be used by physical therapists in order to objectively quantify alterations affecting mainly the thoracic and lumbar regions of the spine, and to establish the criteria for planning and following up their interventions13, the aims of the present study are to investigate (1) the accuracy of the angles of the sagittal curvature from the thoracic and lumbar regions of the spine obtained using an instrument adapted from the arcometer developed by D’Osualdo, Schierano and Iannis18 by comparing them with those obtained using X-ray examination and (2) the inter-evaluator reproducibility and the intraevaluator reproducibility of the arcometer.
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