Health care quality in nonparametric efficiency studies: a review

Scientists are increasingly considering quality in nonparametric frontier efficiency studies in health care. There are many ways to include quality in efficiency analyses. These approaches differ, among other things, in the underlying assumptions about the influence of quality on the attainable efficiency frontier and the distribution of inefficiency scores. The aim is to provide an overview of how scholars have taken quality into account in nonparametric frontier efficiency studies and, at the same time, to address the underlying assumptions on the relationship between efficiency and quality. To this end, we categorized empirical efficiency studies according to the methodological approaches and quality dimensions and collected the quality indicators used. We performed a Web of Science search for studies published in journals covered by the Science Citation Index Expanded, the Social Sciences Citation Index, and the Emerging Sources Citation Index between 1980 and 2020. Of the 126 studies covered in this review, 78 are one-stage studies that incorporate quality directly into the efficiency model and thus assume that quality impacts the attainable efficiency frontier. Forty-four articles are two-stage studies that consider quality in the first and the second stage or the second stage only. Four studies do not assume a priori a specific association between efficiency and quality. Instead, they test for this relationship empirically. Outcome quality is by far the most frequently incorporated quality dimension. While most studies consider structural quality as an environmental variable in the second stage, they include outcome quality predominantly directly in the efficiency model. Process quality is less common.