The Quality of Life Scale (QOLS): Reliability, Validity, and Utilization, 2003, Burkhardt and Anderson

Abstract
The Quality of Life Scale (QOLS), created originally by American psychologist John Flanagan in the 1970's, has been adapted for use in chronic illness groups. This paper reviews the development and psychometric testing of the QOLS.

A descriptive review of the published literature was undertaken and findings summarized in the frequently asked questions format.

Reliability, content and construct validity testing has been performed on the QOLS and a number of translations have been made.

The QOLS has low to moderate correlations with physical health status and disease measures.

However, content validity analysis indicates that the instrument measures domains that diverse patient groups with chronic illness define as quality of life.

The QOLS is a valid instrument for measuring quality of life across patient groups and cultures and is conceptually distinct from health status or other causal indicators of quality of life.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC269997/

Posting because 'improvement in QOL' seems to be repeatedly used to claim success for psychotherapy studies where outcome measures have failed to show effectiveness.
eg TC, RMM research.