The Quality of Life In Depression Scale (QLDS), originally proposed by Sonja Hunt and Stephen McKenna, is a disease specific patient-reported outcome which assesses the impact that depression has on a patient's quality of life. It is the most commonly used measure of quality of life in clinical trials and studies of depression. The QLDS was developed as a measure to be used in future clinical trials of anti-depressant therapy.
It is a 34 item self-rated questionnaire which consists of dichotomous response questions, with the response being either True/Not True. It is scored binomially (0-1) with higher scores on the QLDS indicating a lower quality of life. Several tests of construct validity and internal consistency have found the QLDS to be a good measure of quality of life.
Needs-based model
The QLDS is built around the generally accepted assumption that one's quality of life can only be assessed subjectively. Quality of life tends to be greatly influenced by factors such as depression, anxiety, tension or fatigue.
The QLDS is based around the needs-based model of quality of life. This is derived from the assumption that quality of life is dependent on a person's ability to fulfil particular human needs. The QLDS questions centre around a number of needs that were considered crucial in order to suffice a high quality of life. These include but are not limited to; food, sleep, sex, safety, love, enjoyment, self-esteem and self-actualization.
The QLDS uses a two-point response system with either True or Not True. The high number of items in the questionnaire allows the detection of moderately minor changes in quality of life.
Items on the QLDS are given a score of 1 when the question is applicable to the respondent and 0 when it is not applicable. The items are totalled to give a score ranging from 0–34. Low scores act as an indicator towards a high quality of life.
Development
The QLDS was developed by Galen Research in 1992 and was funded by Lilly Industries. It was developed in the United Kingdom in conjunction with the Netherlands. The QLDS was the first quality of life instrument to be developed in 2 languages simultaneously. The development of the QLDS coincided with a rising interest on the impact of illness and its treatment on the quality of life of the patient. McKenna and Hunt constructed the QLDS on the basis of providing a measure for this, as well as attempting to overcome contemporary studies concerning low correlations between patient self-assessment and nurse or therapist evaluations.
The items in the UK English QLDS were derived from statements made in qualitative interviews by 30 depressed or recently recovered patients based in the North West of England and Scotland. Interviews took a conversational approach and lasted between 30 minutes to 2 hours. Interviewees were between the age range of 19–64 years, with 22 females and 8 males. After a refinement process, based on categories of needs proposed by McKenna and Hunt, 426 relevant statements were derived from the interview transcripts. Upon further scrutinization they produced 41 statements for an initial questionnaire.
A further 35 patients were asked to complete the draft questionnaire and review their experience with it. They were composed of 22 females and 13 males in the age range of 24–72 years. Interviewees expressed a great degree of approval with the questionnaire, although a few mentioned how the binomial system caused difficulty, as it required them to make complete choices.
Following this, the questionnaire was revised to 34 items and field tested to determine construct validity and reliability.
International development
The first two languages the QLDS was available in were UK English and Dutch. These were shown to have good reliability, validity and responsiveness. In 1999, McKenna in collaboration with a team of international researchers developed and tested the QLDS in 9 new languages. This involved translation, followed by field testing for content validity and the new measure's construct validity.