Studying a Study and Testing a Test: How to Read the Medical Evidence PDF
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P1:IML/SBA P2:IML/SBA QC:IML/SBA T1:IML Riegelman-FM Riegelman-1490G Riegelman-v9.cls September1,2004 22:56 Studying a Study and Testing a Test How to Read the Medical Evidence FifthEdition RichardK.Riegelman,m.d.,m.p.h.,phh.d. ProfessorofEpidemiology-Biostatistics,Medicine,andHealthPolicy andFoundingDean TheGeorgeWashingtonUniversity SchoolofPublicHealthandHealthServices Washington,D.C. i P1:IML/SBA P2:IML/SBA QC:IML/SBA T1:IML Riegelman-FM Riegelman-1490G Riegelman-v9.cls September1,2004 22:56 AcquisitionsEditor:DanetteSomers ManagingEditor:MichelleM.LaPlante ProjectManager:BridgettDougherty SeniorManufacturingManager:BenRivera MarketingManager:KathyNeely CoverDesigner:HollyMcLaughlin Compositor:TechBooks Printer:EdwardsBrothers (cid:2)C 2005byRichardK.Riegelman PublishedbyLippincottWilliams&Wilkins 530WalnutStreet Philadelphia,PA19106USA LWW.com Allrightsreserved.Thisbookisprotectedbycopyright.Nopartofthisbookmaybe reproducedinanyformorbyanymeans,includingphotocopying,orutilizedbyany informationstorageandretrievalsystemwithoutwrittenpermissionfromthecopyright owner,exceptforbriefquotationsembodiedincriticalarticlesandreviews.Materials appearinginthisbookpreparedbyindividualsaspartoftheirofficia dutiesasU.S. governmentemployeesarenotcoveredbytheabove-mentionedcopyright. PrintedintheUSA LibraryofCongressCataloging-in-PublicationData <COMP:setCIPhere> Carehasbeentakentoconfir theaccuracyoftheinformationpresentedandtodescribe generallyacceptedpractices.However,theauthors,editors,andpublisherarenot responsibleforerrorsoromissionsorforanyconsequencesfromapplicationofthe informationinthisbookandmakenowarranty,expressedorimplied,withrespecttothe currency,completeness,oraccuracyofthecontentsofthepublication.Applicationofthis informationinaparticularsituationremainstheprofessionalresponsibilityofthe practitioner. Theauthors,editors,andpublisherhaveexertedeveryefforttoensurethatdrugselection anddosagesetforthinthistextareinaccordancewithcurrentrecommendationsand practiceatthetimeofpublication.However,inviewofongoingresearch,changesin governmentregulations,andtheconstantfl wofinformationrelatingtodrugtherapyand drugreactions,thereaderisurgedtocheckthepackageinsertforeachdrugforanychange inindicationsanddosageandforaddedwarningsandprecautions.Thisisparticularly importantwhentherecommendedagentisaneworinfrequentlyemployeddrug. SomedrugsandmedicaldevicespresentedinthispublicationhaveFoodandDrug Administration(FDA)clearanceforlimiteduseinrestrictedresearchsettings.Itisthe responsibilityofthehealthcareprovidertoascertaintheFDAstatusofeachdrugor deviceplannedforuseintheirclinicalpractice. 10 9 8 7 6 5 4 3 2 1 ii P1:IML/SBA P2:IML/SBA QC:IML/SBA T1:IML Riegelman-FM Riegelman-1490G Riegelman-v9.cls September1,2004 22:56 Contents Preface:PuttingProgressIntoPractice v Acknowledgments vii 1. IntroductionandFlaw-CatchingExercise 1 SectionI.StudyingaStudy 2. TypesofStudiesandtheM.A.A.R.I.E.Framework 7 3. Method 16 4. Assignment 20 5. Assessment 25 6. Results 32 7. Interpretation 50 8. Extrapolation 58 9. RandomizedClinicalTrials 67 10. DatabaseResearch:NonconcurrentCohortStudies 89 11. Meta-analysis 99 12. QuestionstoAskandFlaw-CatchingExercises 116 SectionII.TestingaTest 13. Method 137 14. Assignment 143 15. Assessment 149 16. Results 157 17. Interpretation 164 18. Extrapolation 172 19. Screening 175 20. QuestionstoAskandFlaw-CatchingExercises 184 iii P1:IML/SBA P2:IML/SBA QC:IML/SBA T1:IML Riegelman-FM Riegelman-1490G Riegelman-v9.cls September1,2004 22:56 iv Contents SectionIII.RatingaRate 21. MethodandAssignment 193 22. Assessment 200 23. Results 204 24. InterpretationandExtrapolation 211 25. LifeExpectancy 220 26. QuestionstoAskandFlaw-CatchingExercises 227 SectionIV.ConsideringCostsandEvaluatingEffectiveness 27. IntroductionandMethod 235 28. Assignment 246 29. Assessment 251 30. Results 260 31. Interpretation 269 32. Extrapolation 276 33. QuestionstoAskandFlaw-CatchingExercises 280 SectionV.AGuidetotheGuidelines 34. Method 293 35. Assignment 297 36. Assessment 300 37. Results 302 38. Interpretation 308 39. ExtrapolationandQuestionstoAsk 317 SectionVI.SelectingaStatistic 40. BasicPrinciples 323 41. UnivariableAnalysis 334 42. BivariableAnalysis 341 43. MultivariableAnalysis 350 44. SelectingaStatisticFlowcharts 362 Glossary 369 SubjectIndex 395 P1:IML/SBA P2:IML/SBA QC:IML/SBA T1:IML Riegelman-FM Riegelman-1490G Riegelman-v9.cls September1,2004 22:56 Preface Putting Progress Into Practice Thepracticeofmedicineischangingatunprecedentedspeed.Today’sreason- able assumption is outdated by tomorrow’s evidence. A deluge of data faces usasweconfronttheonslaughtofhealthresearchliterature.Howisthebusy student,residentorpractitionertodealwiththisdilemma?Effcientlyreading theresearchevidenceisthekeytosuccessfullyputtingprogressintopractice. The 5th edition of Studying a Study and Testing a Test: How to Read the Medical Evidence opens up the door to the practice of evidence-based medicine. For the frst time, this new edition provides a unifying structure, the M.A.A.R.I.E. framework, for reading the full range of research articles encountered by students, residents and practitioners of medicine and public health.TheM.A.A.R.I.E.frameworkisthekeytothestep-by-stepquestions- to-askapproachtoeffcientlyreadingthemedicalevidence. TheStudyingaStudyOnlineWebsiteisanintegralpartofthe5thedition. Itcanbefoundonthewebatwww.StudyingaStudy.com.ThisWebsitepro- vides practice using the M.A.A.R.I.E. framework, interactive faw-catching exercises,thefowchartofstatisticsandexamplesofhowtoreadrealjournal articles. The book and the Web site together are designed to be useful to the individualreader,residents’JournalClub,aswellasstudentsandfacultyina widevarietyofclinicalandpublichealthdisciplines. Popularfeaturesfrompreviouseditionshavebeenexpandedinthe5thedition andupdatesadded.AnewsectioncalledAGuidetotheGuidelinesexamines evidence-based recommendations for practitioners. New faw-catching exer- cisesappearthroughoutthebook.Thefowchartofstatisticshasbeenupdated andmoreexamplesadded. The Studying a Study and Testing a Test approach to reading the health research literature aims to help students, residents, and practitioners practice evidence-basedmedicinebuiltuponastrongfoundationofresearchevidence. Theaimistohelpyoueffcientlyreviewjournalarticlesandfeelconfdentin your ability to fnd the faws that so often occur. It is important, however, to rememberthateveryfawisnotfatal.Thegoalistorecognizethelimitations ofresearchandtakethemintoaccountasyouputtheevidenceintopractice. Onefnalwarningbeforeyouproceed.Readingthehealthresearchliterature canbehabitforming.Youmayevenfnditenjoyable. v P1:IML/SBA P2:IML/SBA QC:IML/SBA T1:IML Riegelman-FM Riegelman-1490G Riegelman-v9.cls September1,2004 22:56 vi P1:IML/SBA P2:IML/SBA QC:IML/SBA T1:IML Riegelman-FM Riegelman-1490G Riegelman-v9.cls September1,2004 22:56 Acknowledgements Thechallengesassociatedwithproducingthe5theditionofStudyingaStudyand Testing a Test have been made easier by the support and encouragement I have receivedfromstudents,colleagues,andofcoursethemanyreadersoftheprevious editionsfromaroundtheworld. ThiseditionrequiredwritinganewsectioncalledAGuidetotheGuidelinesas wellasextensivelyrewritingtheTestingaTestandRatingaRatesections.Allof thesebeneftedfromfeedbackfromstudentsattheGeorgeWashingtonUniversity School of Public Health and Health Services as well as the School of Medicine andHealthSciences. The Studying a Study Online Web site is a joint project with my wife Linda. She has a unique ability to understand what technology can add to the learning process,anintuitivesenseofhowtomaketechnologywork,andthepatienceto explainitalltome.Asthe“contentprovider”Iremainresponsibleforwhatever goeswrongonthewebbutshedeservesfullcreditforwhatevergoesright. ThestaffofLippincottWilliamsandWilkinsincludingtheireditorsandwebstaff havebeenessentialtomovingthisprojecttocompletion.ThestaffofTechBooks have made the editing of the 5th edition move very smoothly. I am especially gratefultoLymanLyons,thecopyeditor,whohashelpedensurethateverysentence makessenseandeverywordiscarefullychosen. Writinga5theditionofabookisanespeciallyenjoyableexperienceifitmeans thatyougettobuilduponthepastwhilelookingtothefuture.Thishasbeenthe casewiththe5th editionofStudyingaStudyandTestingaTest.Ihopeyouwill enjoyreadingitasmuchasIenjoyedwritingit. RichardRiegelmanM.D.,M.P.H.,Ph.D. WashingtonD.C.July2004 vii P1:IML/SBA P2:IML/SBA QC:IML/SBA T1:IML Riegelman-FM Riegelman-1490G Riegelman-v9.cls September1,2004 22:56 viii P1:IML/FFX P2:IML/FFX QC:IML/FFX T1:IML GB072-01 Riegelman-1490G Riegelman-v9.cls August30,2004 9:14 1 Introduction and Flaw-Catching Exercise Thetraditionalcourseinreadingthehealthliteratureconsistsof“Here’sTheNew EnglandJournalofMedicine.Readit!”Thisapproachisanalogoustolearningto swimbythetotalimmersionmethod.Somepersonscanlearntoswimthisway, ofcourse,butafewdrown,andmanylearntofearthewater. In contrast to the method of total immersion, you are about to embark on a step-by-step,active-participationapproachtoreadingthemedicalevidence.With thetoolsthatyouwilllearn,youwillsoonbeabletoreadajournalarticlecriti- callyandefficientl .Considerableemphasisisplacedontheerrorsthatcanoccur in the various kinds of studies, but try to remember that not every fl w is fa- tal. The goal of literature reading is to recognize the limitations of a study and then put them into perspective. This is essential before putting the results into practice. Tomakeyourjobeasierweuseacommonframeworktoorganizeourreview ofeachofthetypesofinvestigations.Beforedevelopingandillustratingthecom- ponentsoftheframework,however,letusbeginwithafl w-catchingexercise.A fl w-catchingexerciseisasimulatedjournalarticlecontaininganarrayoferrors in each of the components of the framework. Read the following fl w-catching exerciseandthentrytoanswertheaccompanyingquestions. Cries Syndrome: Caused by Television or Just Bad Taste? A medical condition known as Cries syndrome has been described as occurring among children 7 to 9 years old. The condition is characterized by episodes of uninterruptedcryinglastingatleastanhourperdayfor3consecutivedays.The diagnosis also includes symptoms of sore throat, runny nose, and fever which precedes the onset of the crying and are severe enough to keep the child out of school. Investigatorsidentifie 100childrenwithCriessyndrome.ForeachCriessyn- dromechildaclassmatewaschosenforcomparisonfromamongthosewhodid notmissschool.Thestudywasconductedmorethanonemonthaftertheonsetof symptoms. The investigators examined 20 variables, which included all the fac- torstheycouldthinkofasbeingpotentiallyassociatedwithCriessyndrome.They collected data on all medication use, number of spankings, hours of television viewing,andnumberofhoursathome,aswellas16othervariables. Using pictures, they asked the children to identify the medications they had takenwhiletheyhadCriessyndrome.TheirclassmateswithoutCriessyndrome werealsoaskedtousethepicturestoidentifymedicationstakenduringthesame time period. The investigators then asked each child to classify each medica- tion taken as a good-tasting or bad-tasting medication. The data on spankings 1 P1:IML/FFX P2:IML/FFX QC:IML/FFX T1:IML GB072-01 Riegelman-1490G Riegelman-v9.cls August30,2004 9:14 2 Ch.1. IntroductionandFlaw-CatchingExercise wereobtainedfromtheprimarycaregiver.Theinvestigatorsfoundthefollowing data: Percentageofchildrenwhoreportedtakingbad-tastingmedication Criessyndrome: 90% Controls: 10% Averagenumberofspankingsperday Criessyndrome: 1 Controls: 2 Averagenumberoftelevisionviewinghoursperday Criessyndrome: 8(range5to12) Controls: 2(range0to4) Among the 20 variables, analyzed one at a time, the above were the only ones thatwerestatisticallysignifcantusingtheusualstatisticalmethods.Thepvalues were 0.05 except for the hours of television, which had aP-value of 0.001. The investigatorsdrewthefollowingconclusions: 1. Bad-tasting medication is a contributory cause of Cries syndrome because it wasstronglyassociatedwithCriessyndrome. 2. SpankingprotectschildrenfromCriessyndromebecausethecontrolshadan increasedfrequencyofbeingspanked. 3. Television viewing at least 4 hours per day is required for the development of Cries syndrome because all children with Cries syndrome and none of the controlswatchedtelevisionmorethan4hoursperdayduringtheperiodunder investigation. 4. Because Cries syndrome patients were 9 times as likely to take bad-tasting medication,theinvestigatorsconcludedthatremovingbad-tastingmedication fromthemarketwouldeliminatealmost90%ofCriessyndromecasesamong childrenlikethoseinthisinvestigation. 5. Inaddition,regularspankingofallchildren7to9yearsoldshouldbewidely usedasamethodofpreventingCriessyndrome. Nowtogetanideaofwhatyouwillbelearninginthe“StudyingaStudy”section, seeifyoucananswerthefollowingquestions: 1. Whattypeofinvestigationisthis? 2. Whatisthestudyhypothesis? 3. Isthecontrolgroupcorrectlyassigned? 4. Arereportingand/orrecallbiaseslikelytobepresentinthisstudy? 5. Doesthemethodofdatacollectionraiseissuesofprecisionandaccuracy? 6. Istheestimateofthestrengthoftherelationshipperformedcorrectly? 7. Isstatisticalsignifcancetestingperformedcorrectly? 8. Isanadjustmentprocedureneeded? 9. Isanassociationestablishedbetweentheuseofbad-tastingmedicineandCries syndrome? 10. IsitestablishedthatthespankingsoccurredpriortothedevelopmentofCries syndrome? 11. Isitestablishedthatalteringthefrequencyofspankingswillalterthefrequency ofCriessyndrome?
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