Table 155Definitions of summary statistics for diagnostic accuracy studies

MeasureDefinition
True positives (TP)Correct positive test result - number with fibrosis or cirrhosis with a positive index test result
True negatives (TN)Correct negative test results - number without fibrosis or cirrhosis with a negative index test result
False positives (FP)Incorrect positive test result - number without fibrosis or cirrhosis with a positive index test result
False negatives (FN)Incorrect negative test result - number with fibrosis or cirrhosis with a negative index test result
SensitivityProportion of those with the disease (based on reference standard) who are positive on the index test
SpecificityProportion of those without the disease (based on reference standard) who are negative on the index test
Positive predicative value (PPV)Probability of having the disease in a patient with a positive index test result
Negative predicative value (NPV)Probability of not having the disease in a patient with a negative index test result
Positive likelihood ratio (LR+)The number of times more likely a positive test result is in a person with compared to a person without the disease (therefore LR+ is >1)
Negative likelihood ratio (LR−)The number of times more likely a negative test result is in a person with compared to a person without the disease (therefore LR− is <1)

From: 12, Methotrexate and monitoring for hepatotoxicity

Cover of Psoriasis
Psoriasis: Assessment and Management of Psoriasis.
NICE Clinical Guidelines, No. 153.
National Clinical Guideline Centre (UK).
Copyright © National Clinical Guideline Centre - October 2012.

Apart from any fair dealing for the purposes of research or private study, criticism or review, as permitted under the Copyright, Designs and Patents Act, 1988, no part of this publication may be reproduced, stored or transmitted in any form or by any means, without the prior written permission of the publisher or, in the case of reprographic reproduction, in accordance with the terms of licences issued by the Copyright Licensing Agency in the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publisher at the UK address printed on this page.

The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant laws and regulations and therefore for general use.

The rights of National Clinical Guideline Centre to be identified as Author of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act, 1988.

NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.