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The authors declare that they have no competing interests.
MF has initiated, planned and supervised the whole process of the QLiS development, was involved in all phases of the conduct of the study and critically revised the draft of the article. MF was responsible for conducting the studies from step 3 to step 6 and the statistical analyses in these steps and has critically revised the draft of the article. BG made substantial contributions to the conception and design of the whole study and he has been involved in revising the manuscript critically. TM was involved in the planning of stages 2 to 6 and in conducting all stages of the QLiS development including the statistical analyses. He also wrote the first draft of the paper. All authors read and approved the final manuscript.
The aim of the project was to develop an instrument for the assessment of subjective quality of life specific to schizophrenic persons on the basis of patients’ views on their own life and on sound psychometric principles.
The project applied a six-step multiphase development process with six distinct studies. (1) The elicitation of schizophrenic persons’ views on their quality of life was based on open-ended interviews with interviewees from different settings (acute ward inpatients, long-term care patients, community care patients; n = 268). (2) A cross-sectional study with schizophrenic and healthy persons was conducted to quantify the relative importance of the various aspect of quality of life that emerged from the qualitative study (n = 143). (3) We conducted an empirical comparison of response formats with schizophrenic persons (n = 32). (4) A scale construction- and reliability-testing study was performed (n = 203) as well as (5) a test-retest reliability study (n = 49). (6) The final questionnaire (QLiS, quality of life in schizophrenia) was tested in an additional study on convergent and discriminant validity (n = 135).
The QLiS comprises 52 items (plus 2 optional items related to work) in 12 subscales: social contacts, appreciation by others, relationship to family, appraisal of pharmacotherapy, appraisal of psychopathological symptoms, cognitive functioning, abilities to manage daily living, appraisal of accommodation/housing, financial situation, leading a ’normal‘ life, confidence, general life-satisfaction. An item response format with four response categories was preferred by the schizophrenic persons. The mean values of the subscales clustered around the theoretical mean of the subscales and only minimal ceiling effects were found. The reliability (test-retest-reliability and internal consistency) was with one exception > .70 for all subscales.
Taking the low numbers of items per subscale into account, the QLiS can be regarded as an accurate assessment instrument of subjective quality of life in schizophrenia with good content validity.