title: Placebo effect in the treatment of duodenal ulcer.
abstract: OBJECTIVE
  To assess whether frequency of placebo administration is associated with duodenal ulcer healing.
  
  
  METHODS
  A systematic literature review of randomized clinical trials was undertaken. 79 of 80 trials that met the inclusion criteria. The pooled 4 week placebo healing rate of all duodenal ulcer trials that employed a four times a day regimen was compared with the rate obtained from trials with a twice a day regimen.
  
  
  RESULTS
  The pooled 4 week healing rate of the 51 trials with a four times a day regimen was 44. 2% (805 of 1821 patients) compared with 36.2% (545 of 1504 patients) in the 28 trials with a twice a day regimen (difference, 8.0% [equal effects model]; 95% confidence interval, 4.6% to 11.3%). Depending on the statistical analysis, the rate difference ranged from 6.0% (multivariable random effects model) to 8.0% (equal effects model). A number of sensitivity analyses showed comparable differences between the two regimens. Most of these sensitivity analyses were not significant, probably because a number of trials were excluded resulting in a loss of power.
  
  
  CONCLUSIONS
  We found a relation between frequency of placebo administration and healing of duodenal ulcer. We realize that the comparison was based on nonrandomized data. However, we speculate that the difference between regimens was induced by the difference in frequency of placebo administration. A better knowledge of various placebo effects is required in order to make clinically relevant assessments of treatment effects derived from placebo-controlled trials.
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, Academic Medical Center, University of Amsterdam, The Netherlands. AJMdeCraen@epi.azl.nl
authors.forename: A J
authors.initials: AJ
authors.lastname: de Craen
authors.forename: D E
authors.initials: DE
authors.lastname: Moerman
authors.forename: S H
authors.initials: SH
authors.lastname: Heisterkamp
authors.forename: G N
authors.initials: GN
authors.lastname: Tytgat
authors.forename: J G
authors.initials: JG
authors.lastname: Tijssen
authors.forename: J
authors.initials: J
authors.lastname: Kleijnen
mesh_terms: D004381:Duodenal Ulcer / Q000188:drug therapy*; D005765:Gastrointestinal Agents / Q000627:therapeutic use; D006801:Humans; D015233:Models, Statistical; D015990:Placebo Effect; D010919:Placebos; D016032:Randomized Controlled Trials as Topic
chemical_list: D005765:Gastrointestinal Agents; D010919:Placebos