Table 4Best study design to answer each type of question

Type of questionBest primary study design
Effectiveness or other impact of an interventionRCT; other studies that may be considered in the absence of an RCT are the following: internally/externally controlled before and after trial, interrupted time-series
Accuracy of information (for example, risk factor, test, prediction rule)Comparing the information against a valid gold standard in a randomised trial or inception cohort study
Rates (of disease, patient experience, rare side effects)Cohort, registry, cross-sectional study


Cover of Depression in Adults with a Chronic Physical Health Problem
Depression in Adults with a Chronic Physical Health Problem: Treatment and Management.
NICE Clinical Guidelines, No. 91.
National Collaborating Centre for Mental Health (UK).
Leicester (UK): British Psychological Society; 2010.
Copyright © 2010, The British Psychological Society & The Royal College of Psychiatrists.

All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. Enquiries in this regard should be directed to the British Psychological Society.

PubMed Health. A service of the National Library of Medicine, National Institutes of Health.