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1、Frederick L. Brancati, MD, MHSProfessor of Medicine & EpidemiologyDirector, Division of General Internal MedicineOsler Journal Club 2006Visit Hopkins GIM at http:/www.hopkinsmedicine.org/gimProspective Cohort Studies.BackgroundPhysical activity lower CVD riskDHHS recommends life-long pursuitsSports
2、differ in sustainabilityCVD benefits of individual sports uncertain. The Johns Hopkins Precursors StudyOver 1300 students (mainly white men) from the JHUSOM Classes of 1948-64. Baseline data collected in person in medical school. Follow-up data collected by yearly mailed questionnaires thereafter.Ca
3、roline Thomas, MDThe Johns Hopkins Precursors Study.Hypothesis: Tennis ability in youth predicts lower CVD risk in middle ageDesign: Prospective cohort studySetting: Johns Hopkins Precursors StudyParticipants: 1019 male medical studentsData Collection: Extensive interview and physical assessment at
4、baseline (early 20s); annual mailed follow-up questionnairesOutcome: Incident CVD, including MI, CHD, CABG or PTCA, hypertensive heart disease, heart failure, & cerebrovascular diseaseAnalysis: Kaplan-Meier, Cox modelsOutline.Assessment of Sports AbilityHow would you rate your overall ability in ten
5、nis (golf, football, baseball, basketball) during and before medical school?No abilityPoor or fair abilityGood or excellent abilityNo data on frequency, intensity, or subsequent participation.Results.Conclusions / ImplicationsSelf-described tennis ability in young adulthood predicts lower CVD risk i
6、n middle ageAssociation of tennis to lower risk isGraded (i.e. dose-response)Independent of many possible confoundersSpecific to tennis (as hypothesized)Suggests promotion of tennis as a means to reduce CVD risk.StrengthsProspective designLong-term follow-upMultiavariate analysisBlinded assessment o
7、f CVD.WeaknessesObservational studies cant prove causalityResidual confounding is likelyAssessment of exposure was suboptimalAbility, not activitySingle point, not repeated measuresSelf-assessed, not objectiveSample limits generalizability.Discussion PointsWhats special about a cohort study?What are
8、 common obstacles?Can it be used for housestaff research?Can it ever be sufficient to change practice?How do cohort studies relate to outcomes research? .Taxonomy of DesignsRandomized Controlled TrialProspective Cohort StudyCase-Control StudyCross-Sectional StudyOther DesignsQuasi-ExperimentalEcolog
9、ic Case Report.The basic fighting unit was a cohort, composed of six centuries (480 men plus 6 centurions). The legion itself was composed of ten cohorts, and the first cohort had many extra menthe clerks, engineers, and other specialists who did not usually fightand the senior centurion of the legi
10、on, the primipilus, or “number one javelin.” .prospective Pronunciation: pr&-spek-tiv also pr-, prO-, pr-Function: adjectiveDate: circa 16991 : relating to or effective in the future2 a : likely to come about : EXPECTED b : likely to be or become .“Prospective” in EpidemiologyClearly defined cohort
11、(group, sample) of persons at risk followed through timeData regarding exposures (risk factors, predictors) collected prior to data on outcomes (endpoints)Research-grade data collection methods used for purpose of testing hypothesis (?).Diagram of Hypothetical 6-Year Cohort Study to Identify Risk Fa
12、ctors for Facial Acne in Teenagers1000 12-year-olds without acne500 18-year-olds without acne900 15-year-olds without acne50 with Acne300 with Acne5 moved10 no answer35 refused10 moved40 no answer48 refused 2 deaths350 incident cases of acne over 6 years6-yr Follow-up Rate = 850/1000 = 85%Incidence
13、Rate of Acne = 350/5475 PY = 63.9 per 1000 PY.Why Do A Cohort Study?Get incidence dataStudy a range of possible risk factorsEstablish temporal sequenceGet representative dataPrepare for randomized controlled trialEstablish a research empire.Types of CohortsOccupational (e.g. Asbestos workers)Conveni
14、ence (e.g. Precursors, Nurses)Geographic (e.g. Framingham, ARIC)Disease or ProcedureNatural History (e.g. Syncope, Lupus)Outcomes Research (e.g. Dialysis, Cataracts).Sources of Cohort DataClinic VisitsLaboratory AssaysInterviewPhysical ExaminationImaging Physiologic testsHome visitsMailed materialsT
15、elephone InterviewMedical RecordsAdministrative DataMedicareMedicaidManaged CareVeterans AdminBirth RecordsDeath CertificatesSpecimen Bank.William Castelli, MDThe Framingham Heart Study.Recently Published Studies from the Johns Hopkins Precursors StudyCoronary Disease -Anger, Depression, Gout, -Spor
16、ts AbilityType 2 Diabetes -Blood pressure, AdiposityHypertension -CoffeeKnee Osteoarthritis -Knee injuryDepression -InsomniaOutcomeExposure.What Might Explain Observed Relationship of Tennis Ability to Heart Disease Risk?Tennis protects against heart diseaseMen who like to play tennis are differentT
17、hinnerHealthier LifestylesHigher Socioeconomic StatusMen who play tennis well are differentTaller, ThinnerGreater Cardiovascular FitnessChance (type I error) Needs confirmation.Plays TennisPlays Tennis WellSustained Activity Thru MidlifeLower adiposity, Greater FitnessLower BP, Lower LDL, Higher HDL
18、Lower Risk of CHD Hypothetical Causal PathwayHealthier Men Choose TennisHealthier Men Play Tennis WellPotential Confounders.Grey HairHigher Risk of CHDHypothetical Causal PathwayOlder AgePotential Confounders.Challenges in Cohort StudiesPossibly long durationPossibly large sample sizeNeed to recruit
19、 people “at risk”Drop outs, Deaths, Other lossesConcern about residual confoundingMultiple comparisons Type I error.How to Exploit Cohort Design When Time is Short & Money is ScarceAnalyze existing data from another studyPiggy-back onto on-going studyChoose hospital-based cohortChoose short-term outcomeConsider administrative dataConsider public-use dataConsider non-concurrent design.
