title: Calendar rhythm efficacy: a review.
abstract: OBJECTIVE
  To estimate the unplanned pregnancy rate of calendar rhythm.
  
  
  METHODS
  Meta-analysis of eight studies of calendar rhythm published between 1940 and 1989.
  
  
  RESULTS
  There exist few studies of the calendar rhythm method. Analysis of the best of these studies resulted in a conservative estimated Pearl rate of 18.5 +/- 1.8, and a less conservative estimate of 15.0 +/- 4.0, standardized to 12 months' observation; these results are in the range of other natural and barrier methods.
  
  
  CONCLUSIONS
  We need properly done clinical trials of the calendar rhythm method to scientifically establish its effectiveness.
authors.affiliation: Department of Population Dynamics, Johns Hopkins School of Hygiene and Public Health, Baltimore, MD 21205, USA.
authors.forename: R T
authors.initials: RT
authors.lastname: Kambic
authors.forename: V
authors.initials: V
authors.lastname: Lamprecht
mesh_terms: D005260:Female; D006801:Humans; D012252:Natural Family Planning Methods; D010061:Ovulation Detection / Q000379:methods; D010507:Periodicity; D011247:Pregnancy / Q000502:physiology / Q000706:statistics & numerical data*; D018873:Pregnancy Rate; D015203:Reproducibility of Results