Example: confidence

Cover 4/23/05 5:33 PM Page i

Cover 4/23/05 5:33 PM Page iFlow charts indicating appropriate techniques in different circumstances*Flow chart for hypothesis testsNumerical data1 group2 groups>2 groupsOne-samplet-test (19)Sign test (19)PairedIndependentIndependent1 group2 groups>2 groupsChi-squaredtest (25)Categorical data2 categories(investigatingproportions)>2 categoriesPaired t -test (20)Sign test (19)Wilcoxon signedranks test (20)Unpairedt -test (21)Wilcoxon ranksum test (21)One-wayANOVA (22)Kruskal-Wallistest (22)z test for aproportion (23)Sign test (23)PairedChi-squaredtest (25)Chi-squaredtrend test (25)IndependentMcNemar stest (24)Chi-squaredtest (24)Fisher s exacttest (24)*Relevant chapter numbers shown in chart for further analysesRegressionmethodsLongitudinalstu diesAdditionaltopicsCorrelationRegressio nLogistic (30)Poisson (31)Repeated measures (41 42)Survival analysis (44)Evidence-based medicine (40)

Sampling and estimation 10 Sampling and sampling distributions 26 11 Confidence intervals 28 Study design 12 Study design I 30 13 Study design II 32 14 Clinical trials 34 15 Cohort studies 37 16 Case–control studies 40 Hypothesis testing 17 Hypothesis testing 42 18 Errors in hypothesis testing 44 Basic techniques for analysing data Numerical ...

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Transcription of Cover 4/23/05 5:33 PM Page i

1 Cover 4/23/05 5:33 PM Page iFlow charts indicating appropriate techniques in different circumstances*Flow chart for hypothesis testsNumerical data1 group2 groups>2 groupsOne-samplet-test (19)Sign test (19)PairedIndependentIndependent1 group2 groups>2 groupsChi-squaredtest (25)Categorical data2 categories(investigatingproportions)>2 categoriesPaired t -test (20)Sign test (19)Wilcoxon signedranks test (20)Unpairedt -test (21)Wilcoxon ranksum test (21)One-wayANOVA (22)Kruskal-Wallistest (22)z test for aproportion (23)Sign test (23)PairedChi-squaredtest (25)Chi-squaredtrend test (25)IndependentMcNemar stest (24)Chi-squaredtest (24)Fisher s exacttest (24)*Relevant chapter numbers shown in chart for further analysesRegressionmethodsLongitudinalstu diesAdditionaltopicsCorrelationRegressio nLogistic (30)Poisson (31)Repeated measures (41 42)Survival analysis (44)Evidence-based medicine (40)Systematic reviews andmeta-analyses (43)Diagnostic tools sensitivity, specificity (38)Agreement kappa (39)Bayesian methods (45)Correlation coefficientsPearson s (26)Spearman s (26)Simple (27 28)Multiple (29)Logistic (30)Poisson (31)Modelling (32 34)Cluster (42)

2 AssessingevidenceCover 4/23/05 5:33 PM Page iiMedical Statistics at a GlancePMAPR 4/23/05 6:32 PM Page 1 PMAPR 4/23/05 6:32 PM Page 2 Medical Statistics at a GlanceAviva PetrieHead of Biostatistics Unit and Senior LecturerEastman Dental InstituteUniversity College London256 Grays Inn RoadLondon WC1X 8LD andHonorary Lecturer in Medical StatisticsMedical Statistics UnitLondon School of Hygiene and Tropical MedicineKeppel StreetLondon WC1E 7 HTCaroline SabinProfessor of Medical Statistics and EpidemiologyDepartment of Primary Care and Population SciencesRoyal Free and University College Medical SchoolRowland Hill StreetLondon NW3 2 PFSecond editionPMAPR 4/23/05 6.

3 32 PM Page 3 2005 Aviva Petrie and Caroline SabinPublished by Blackwell Publishing LtdBlackwell Publishing, Inc., 350 Main Street, Malden, Massachusetts 02148-5020, USAB lackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UKBlackwell Publishing Asia Pty Ltd, 550 Swanston Street, Carlton, Victoria 3053, AustraliaThe right of the Authors to be identified as the Authors of this Work has been asserted in accordance with theCopyright, Designs and Patents Act rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise,except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the published 2000 Reprinted 2001 (twice), 2002, 2003 (twice), 2004 Second edition 2005 Library of Congress Cataloging-in-Publication DataPetrie, statistics at a glance / Aviva Petrie, Caroline Sabin.

4 2nd ; : 978-1-4051-2780-6 (alk. paper)ISBN-10: 1-4051-2780-5 (alk. paper)1. Medical statistics.[DNLM:1. Research Design. WA 950 P495m 2005]I. Sabin, 2005610 .72 dc222004026022 ISBN-13: 978-1-4051-2780-6 ISBN-10: 1-4051-2780-5 Acatalogue record for this title is available from the British LibrarySet in 9 pt Times by SNP Best-set Typesetter Ltd., Hong KongPrinted and bound in India by Replika Press Pvt. Editor: Martin SugdenDevelopment Editor: Karen MooreProduction Controller: Kate CharmanFor further information on Blackwell Publishing, visit our website: publisher s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp processed using acid-free and elementary chlorine-free practices.

5 Furthermore, the publisher ensures that the text paper and Cover board used have met acceptableenvironmental accreditation 4/23/05 6:32 PM Page 424 Categorical data: two proportions 6125 Categorical data: more than two categories 64 Regression and correlation26 Correlation 6727 The theory of linear regression 7028 Performing a linear regression analysis 7229 Multiple linear regression 7630 Binary outcomes and logistic regression 7931 Rates and Poisson regression 8232 Generalized linear models 8633 Explanatory variables in statistical models 8834 Issues in statistical modelling 91 Important considerations35 Checking assumptions 9436 Sample size calculations 9637 Presenting results 99 Additional chapters38 Diagnostic tools 10239 Assessing agreement 10540

6 Evidence-based medicine 10841 Methods for clustered data 11042 Regression methods for clustered data 11343 Systematic reviews and meta-analysis 11644 Survival analysis 11945 Bayesian methods 122 AppendixAStatistical tables 124 BAltman s nomogram for sample size calculations 131 CTypical computer output 132 DGlossary of terms 144 Index 153 Preface 6 Handling data1 Types of data 82 Data entry 103 Error checking and outliers 124 Displaying data graphically 145 Describing data: the average 166 Describing data: the spread 187 Theoretical distributions: the Normal distribution 208 Theoretical distributions: other distributions 229 Transformations 24 Sampling and estimation10 Sampling and sampling distributions 2611 Confidence intervals 28 Study design12 Study design I 3013 Study design II 3214 Clinical trials 3415 Cohort studies 3716 Case control studies 40 Hypothesis testing17 Hypothesis testing 4218 Errors in hypothesis testing 44 Basic techniques for analysing dataNumerical data19 Numerical data: a single group 4620 Numerical data: two related groups 4921 Numerical data.

7 Two unrelated groups 5222 Numerical data: more than two groups 55 Categorical data23 Categorical data: a single proportion 585 ContentsVisit further material including an extensive reference list and multiple choice questions (MCQs) with inter-active answers for 4/23/05 6:32 PM Page 56 Preface Issues in statistical modelling (Chapter 34). We have also modi-fied Chapter 41 which describes different approaches to the analysisof clustered data, and added Chapter 42 which outlines the variousregression methods that can be used to analyse this type of data. The first edition had a brief description of time series analysis which we decided to omit from this second edition as we felt that itwas probably too limited to be of real use, and expanding it wouldgo beyond the bounds of our remit.

8 Because of this omission and thechapters that we have added, the numbering of the chapters in thesecond edition differs from that of the first edition after Chapter of the chapters in this latter section of the book which werealso in the first edition are altered only slightly, if at description of every statistical technique is accompanied byan example illustrating its use. We have generally obtained the datafor these examples from collaborative studies in which we or col-leagues have been involved; in some instances, we have used realdata from published papers. Where possible, we have used the samedata set in more than one chapter to reflect the reality of data analy-sis which is rarely restricted to a single technique or we believe that formulae should be provided and the logicof the approach explained as an aid to understanding, we haveavoided showing the details of complex calculations most readerswill have access to computers and are unlikely to perform any butthe simplest calculations by consider that it is particularly important for the reader to beable to interpret output from a computer package.

9 We have thereforechosen, where applicable, to show results using extracts from com-puter output. In some instances, where we believe individuals mayhave difficulty with its interpretation, we have included (AppendixC) and annotated the complete computer output from an analysis ofa data set. There are many statistical packages in common use; togive the reader an indication of how output can vary, we have notrestricted the output to a particular package and have, instead, usedthree well known ones SAS, SPSS and is extensive cross-referencing throughout the text to helpthe reader link the various procedures.

10 A basic set of statisticaltables is contained in Appendix A. Neave, (1981) Elememen-tary Statistical TablesRoutledge, and Diem, K. (1970) DocumentaGeigy Scientific Tables, 7th Edn, Blackwell Publishing: Oxford,amongst others, provide fuller versions if the reader requires moreprecise results for hand calculations. The Glossary of terms (Appendix D) provides readily accessible explanations of com-monly used know that one of the greatest difficulties facing non-statisticians is choosing the appropriate technique. We have there-fore produced two flow charts which can be used both to aid thedecision as to what method to use in a given situation and to locatea particular technique in the book easily.


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