Nonspecific effects in longitudinal studies: impact on quality of life measures.

  title={Nonspecific effects in longitudinal studies: impact on quality of life measures.},
  author={Christophe Bouchet and Francis Guillemin and Serge Briançon},
  journal={Journal of clinical epidemiology},
  volume={49 1},
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… CONTINUE READING

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