How is quality of life defined and assessed in published research?

To ensure clarity in communication in the field of quality of life research, and meaningful use of 'quality of life' as a research outcome, requires two things: awareness that there is a range of conceptualisations and definitions of 'quality of life', and for any particular study, consistency between the way the term is defined and operationalised in that setting. We aimed to identify how frequently research articles described (HR)QOL as a construct of interest, how frequently they referred to "patient-reported outcome (measures)", which patient-reported outcome measures were used, and how (HR)QOL was defined.

We reviewed all Quality of Life Research articles published in 2017 and recorded whether they described health-related quality of life or quality of life as constructs of interest, and/or mentioned the term(s) patient-reported outcome (measures). We recorded definitions of (HR)QOL stated and questionnaires used. We classified articles according to constructs assessed and instruments used, and examined whether articles citing the same definition used the same questionnaires.

We reviewed 300 articles; 65% stated that (HR)QOL was a construct of interest, 27% mentioned patient-reported outcome (measures), and 20% mentioned neither. Fifty-one articles provided definitions of (HR)QOL, citing 66 sources, with 11 definitions cited more than once. PROMIS, SF, EQ-5D, and EORTC instruments were the most commonly used. The only definition and questionnaire consistently used together were the WHO definitions/instruments.

These results demonstrate considerable heterogeneity in the definition and operationalisation of (HR)QOL, between and within studies. This limits meaningful interpretation of (HR)QOL scores and complicates literature searches. Investigators should define constructs and select instruments aligned with their definitions.