Errors of measurement affecting the reliability and validity of data acquired from self-assessed quality of life.

Research often uses self-assessed quality of life. Quality of life cannot be observed directly; other variables have to serve as its indicators. In the case of self-assessed quality of life, the researcher has to rely upon the individual's own statement as to how she/he feels. The subjective nature of the term creates problems in the matter of reliability and validity of the data thus collected. Random and systematic errors of measurement are liable to influence the result of the investigations. The researcher must know the possible sources of error and make allowances for them if research into quality of life is to be a worthwhile contribution to a greater understanding of what is meant by having a good life, and of the means to achieve it.