Selection of the best outcome measures is a crucial step in psychiatric research. There are excellent instruments available for most areas of interest and researchers are often faced with a confusing choice. Getting it right will save you time and money, affect the validity and comparability of your results and, ultimately, improve the impact of your publications. This booklet, extracted from the third edition of Research Methods in Psychiatry and with a new foreword and introduction, will help guide you through the crucial process of selecting the rating scales to use in your research. Crucially, each scale is listed with its citation rate as a guide to its popularity among the research community and the potential comparability of results.