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.Background Physical activity lower CVD risk DHHS recommends life-long pursuits Sports dif
2、fer in sustainability CVD 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.Caroline
3、Thomas,MDThe Johns Hopkins Precursors Study.Hypothesis:Tennis ability in youth predicts lower CVD risk in middle age Design:Prospective cohort study Setting:Johns Hopkins Precursors Study Participants:1019 male medical students Data Collection:Extensive interview and physical assessment at baseline(
4、early 20s);annual mailed follow-up questionnaires Outcome:Incident CVD,including MI,CHD,CABG or PTCA,hypertensive heart disease,heart failure,&cerebrovascular disease Analysis:Kaplan-Meier,Cox modelsOutline.Assessment of Sports Ability How would you rate your overall ability in tennis(golf,football,
5、baseball,basketball)during and before medical school?No ability Poor or fair ability Good or excellent ability No data on frequency,intensity,or subsequent participation.Results.Conclusions/Implications Self-described tennis ability in young adulthood predicts lower CVD risk in middle age Associatio
6、n of tennis to lower risk is Graded(i.e.dose-response)Independent of many possible confounders Specific to tennis(as hypothesized)Suggests promotion of tennis as a means to reduce CVD risk.Strengths Prospective design Long-term follow-up Multiavariate analysis Blinded assessment of CVD.Weaknesses Ob
7、servational studies cant prove causality Residual confounding is likely Assessment of exposure was suboptimal Ability,not activity Single point,not repeated measures Self-assessed,not objective Sample limits generalizability.Discussion Points Whats special about a cohort study?What are common obstac
8、les?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 Designs Randomized Controlled Trial Prospective Cohort Study Case-Control Study Cross-Sectional Study Other Designs Quasi-Experimental Ecologic Case
9、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 legion,the primipi
10、lus,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 Epidemiology Clearly defined cohort(group,sample)of persons at risk
11、 followed through time Data 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 Factors for Facial Acne in Teenagers1000
12、 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 Rate of Acne=350/5475 PY=63.9 per 1000 PY.
13、Why Do A Cohort Study?Get incidence data Study a range of possible risk factors Establish temporal sequence Get representative data Prepare for randomized controlled trial Establish a research empire.Types of Cohorts Occupational(e.g.Asbestos workers)Convenience(e.g.Precursors,Nurses)Geographic(e.g.
14、Framingham,ARIC)Disease or Procedure Natural History(e.g.Syncope,Lupus)Outcomes Research(e.g.Dialysis,Cataracts).Sources of Cohort Data Clinic Visits Laboratory Assays Interview Physical Examination Imaging Physiologic tests Home visits Mailed materials Telephone Interview Medical Records Administra
15、tive Data Medicare Medicaid Managed Care Veterans Admin Birth Records Death Certificates Specimen Bank.William Castelli,MDThe Framingham Heart Study.Recently Published Studies from the Johns Hopkins Precursors Study Coronary Disease -Anger,Depression,Gout,-Sports Ability Type 2 Diabetes -Blood press
16、ure,Adiposity Hypertension -Coffee Knee Osteoarthritis -Knee injury Depression -InsomniaOutcomeExposure.What Might Explain Observed Relationship of Tennis Ability to Heart Disease Risk?Tennis protects against heart disease Men who like to play tennis are different Thinner Healthier Lifestyles Higher
17、 Socioeconomic Status Men who play tennis well are different Taller,Thinner Greater Cardiovascular Fitness Chance(type I error)Needs confirmation.Plays TennisPlays Tennis WellSustained Activity Thru MidlifeLower adiposity,Greater FitnessLower BP,Lower LDL,Higher HDLLower Risk of CHD Hypothetical Cau
18、sal PathwayHealthier Men Choose TennisHealthier Men Play Tennis WellPotential Confounders.Grey HairHigher Risk of CHDHypothetical Causal PathwayOlder AgePotential Confounders.Challenges in Cohort Studies Possibly long duration Possibly large sample size Need to recruit people“at risk”Drop outs,Death
19、s,Other losses Concern about residual confounding Multiple comparisons Type I error.How to Exploit Cohort Design When Time is Short&Money is Scarce Analyze existing data from another study Piggy-back onto on-going study Choose hospital-based cohort Choose short-term outcome Consider administrative data Consider public-use data Consider non-concurrent design.Cohort Assembled&Data CollectedYou Get the Ideato Do Follow-upExposedUnexposedt=0Someone Else Does the Hard WorkYearsLaterDeath,Diseaes,Other OutcomesNon-Concurrent Prospective Cohort Study.
