Original article
Nonspecific effects in longitudinal studies: Impact on quality of life measures

https://doi.org/10.1016/0895-4356(95)00540-4Get rights and content

Abstract

A variety of factors may influence outcome measures in longitudinal studies, including placebo, Hawthorne, or natural history effects. Quality of life (Qol) measures are particularly subject to these phenomena. This 2-month postal survey was set up to examine the extent of nonspecific effects in a treatment (vitamin supplementation) group (n = 180), a placebo group (n = 180), as part of a stratified, randomized controlled trial, and two control groups (n = 768 each). Quality of life was measured using the SF36. The placebo effect had a significant impact on improving physical, mental, and pain dimensions (p = 0.02 to 0.04), and the Hawthorne effect was significant (p = 0.03 to 0.009) for psychological dimensions. Although the impact of natural history was not significant, it tended to worsen all QoL dimensions. Vitamin supplementation had no effect on QoL. These results demonstrate the importance of placebo and Hawthorne effects and suggest that they may be responsible for misleading results or reductions in the power of controlled trials.

References (28)

  • P Knipschild et al.

    The qualification period

    J Clin Epidemiol

    (1991)
  • I Wiklund et al.

    Factors of importance when evaluating quality of life in clinical trials

    Contr Clin Trials

    (1990)
  • DL Streiner et al.

    PDQ Epidemiology

  • AK Shapiro

    Factors contributing to the placebo effect: Their implications for psychotherapy

    Am J Psychother

    (1961)
  • RH Fletcher et al.

    Clinical Epidemiology: The Essentials

  • JA Turner et al.

    The importance of placebo effects in pain treatment and research

    JAMA

    (1994)
  • AE Fletcher et al.

    Measurement of quality of life in clinical trials of therapy

    Cardiology

    (1988)
  • GH Guyatt et al.

    Measuring quality of life in clinical trials: A taxonomy and review

    Can Med Assoc J

    (1989)
  • R Fitzpatrick et al.

    Quality of life measures in health care. I. Applications and issues in assessment

    Br Med J

    (1992)
  • S Hercberg et al.

    Le projet SU.VI.MAX: 100 000 volontaires pour la recherche en nutrition dans le domaine de la prévention

    Cah Nutr Diét

    (1993)
  • AL Stewart et al.

    The MOS short form general health survey

    Med Care

    (1988)
  • CA McHorney et al.

    The MOS 36-Item Short-Form Health Survey (SF-36). II. Psychometric and clinical tests of validity in measuring physical and mental health constructs

    Med Care

    (1993)
  • CA McHorney et al.

    The MOS 36-item Short-Form Health Survey (SF-36). III. Tests of data quality, scaling assumptions, and reliability across diverse patient groups

    Med Care

    (1994)
  • NK Aaronson et al.

    International quality of life assessment (IQOLA) project

    Qual Life Res

    (1992)
  • Cited by (0)

    View full text