Thanks are due to Dr Andersch, Professor Lorrainee Dennerstein, Dr E. W. Freeman, Dr P. J. Magill, Dr Andrea Rapkin, Dr S. S. Shapiro, Dr S. L. Smith and Dr Wendy Vanselow who answered questions about the methods used in their trials.

Ferring Pharmaceuticals, Berkshire, UK, Nordic Pharma UK Ltd and Wyeth Pharmaceuticals UK answered questions about progesterone products and unpublished material.

The staff of the Yeovil Central Branch of Somerset County Council Library took meticulous care in tracing obscure journals and inter‐library loans. Rose Elliot, Jill Lang, Jean Robinson and Dawn Robson deserve special thanks for this work.

Thanks are due also to Jean Hill formerly of the Academy Library, Somerset Academy‐Yeovil, Yeovil District Hospital for help with searches and copies of journal articles.

We are grateful for the support given by the staff of the Menstrual Disorders and Subfertility Group, especially Michelle Proctor, former Review Group Co‐ordinator,and the Search Co‐ordinators.

We thank Peter Gotzsche of the Nordic Cochrane Centre, Andy Vail, Manchester University and Sofia Dias, University of Bristol for advice on presenting data.

We acknowledge help with the assessment of the selective outcome domain in the Risk of Bias Tables, from Jamie Kirkham of the MRC funded project Outcome Reporting Bias in Trials (G0500952) investigating the degree and impact of outcome reporting bias in Cochrane reviews.