Introduction

Systematic reviews are made for many different types of studies, such as randomized clinical trials (RCTs), observational studies and diagnostic studies. Researchers, doctors and policy-makers use the results and conclusions of systematic reviews for research purposes, development of guidelines, and evidence-based patient care and policy-making. It saves them a considerable amount of time in searching for literature, and reading and interpreting the relevant articles. For the same purposes, more and more systematic reviews of studies focusing on the measurement properties of measurement instruments are being published. The aim of such reviews is to find all the existing evidence of the properties of one or more measurement instruments, to evaluate the strength of this evidence, and come to a conclusion about the best instrument available for a particular purpose. They may also result in a recommendation for additional research.