Sample sizes for studies using the short form 36 (SF-36)

نویسندگان

  • S A Julious
  • S George
  • M J Campbell
چکیده

When designing a study to compare the outcomes of an intervention, an essential step is the calculation of sample sizes that will allow a reasonable chance (power) of detecting a predetermined difference (effect size) in the outcome variable, at a given level of significance. Sample size is critically dependent on the proposed effect size: half the effect size and the sample size is quadrupled. Unlike power and level ofsignificance, for which norms and precedents dictate values, the effect size must be determined from experience, published data, or pilot studies. It is variously defined as the "minimum value worth detecting" or a "clinically important effect", or "quantitatively significant effect"..1 The short form 36 (SF-36) health survey questionnaire is a multi-dimensional measure of perceived health status originally developed in the USA.2 It has been adapted for use in UK populations,3 and UK population norms have recently been made available for adults of working age.4 The SF-36 has been compared in "normal" populations with the Nottingham health profile,3 and has been reported to be preferable for measuring improvements in health in a population with relatively minor conditions such as in general practice or in the community. This is because more subjects use a wider range of scores, which leads to a greater power to discriminate between groups. This variation has lead Ziebland to suggest that it is an inadequate tool to assess health interventions aimed at heterogeneous communities.5 Scores have been quoted as means and standard deviations, implying that parametric methods should be used to estimate sample sizes,4 and indeed this is the methodology recommended in the SF-36 manual.6 However, the distributions of SF-36 dimension scores are not "normal".3 This paper highlights discrepancies between sample sizes for intervention studies using the SF-36 calculated using conventional parametric techniques7 and a non-parametric approach.8

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عنوان ژورنال:
  • Journal of epidemiology and community health

دوره 49 6  شماره 

صفحات  -

تاریخ انتشار 1995