Efficacy calculation in randomized trials: Global or local measures?

Michael Emch, Mohammad Ali, Camilo Acosta, Mohammad Yunus, David A. Sack, John D. Clemens

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


This study tests whether the effect of a vaccine trial varies in space and why. Analytical z-score maps identify unusually high- and low-efficacy values in a trial area. Relationships between neighborhood efficacy and ecological variables are measured to explain why efficacy varies in space. Efficacy was found to vary regardless of neighborhood size and the variation is related to several ecological determinants. Local efficacy measures can help public health practitioners make better decisions about when and where to vaccinate populations. The concepts offered in this study are pertinent for any health intervention trial, not just vaccines.

Original languageEnglish (US)
Pages (from-to)238-248
Number of pages11
JournalHealth and Place
Issue number1
StatePublished - Mar 2007
Externally publishedYes


  • Cholera
  • Herd immunity
  • Intervention trials
  • Neighborhood determinants
  • Spatial analysis
  • Vaccines

ASJC Scopus subject areas

  • Health(social science)
  • Sociology and Political Science
  • Life-span and Life-course Studies


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