Overview of Epidemiological Study


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Overview of Epidemiological Study

  1. 1. 1 NOVEMBER 2003<br />Design 1-11-03<br />1<br />Overview of Epidemiological Study<br />
  2. 2. 2<br />Outline<br /><ul><li>Step of Study
  3. 3. Formulate Questions
  4. 4. Type of Designs
  5. 5. Observational study
  6. 6. Experimental study</li></li></ul><li>3<br />Review Literature<br />Framework Theory<br />Research DESIGN<br />Formulate HypothesisObjective<br />Collect Data<br />Methodology<br />Analyze Data<br />Define Target Population<br />Intervention (if any)<br />Define Variables<br />Determine Measurement<br />Interpret the Results<br />Communicate the Results<br />Main Step of Epidemiological Study/ Research Process<br />FormulatethePROBLEM(S)<br />
  7. 7. Types of Questions<br />Describing natural events<br />Assessing association of observed interesting factors and outcomes<br />Evaluating effect of assigned interesting factor on outcome<br />4<br />
  8. 8. 5<br />Type of Designs<br />Assignedexposure<br />E=Exposure<br />O=Outcome<br />Experimental<br />No comparison group<br />X-sectional<br />Descriptive<br />longitudinal<br />Naturalexposure<br />Observational<br />Cohort<br />(Prospective ; E -> O)<br />Analytical<br />Case-control<br />(Retrospective ; O -> E)<br />With comparison group<br />Cross-sectional<br />(Concurrent ; E/O)<br />
  9. 9. 1 NOVEMBER 2003<br />Design 1-11-03<br />6<br /> “Exposures” and “Outcomes”<br />Experimental studies <br />- Investigator assigns exposure<br /> - Investigator assesses outcome<br />Observational studies <br />- Individualassigns exposure<br /> - Investigator assesses outcome<br />
  10. 10. Results<br />7<br />Results<br />(Data or Fact)<br />Study<br />procedures<br />Questions<br />+<br />True value<br />Error<br />Randomerror<br />(Chance)<br />Systematicerror<br />(Bias)<br />Proper statistics<br />Proper design and methodology<br />
  11. 11. 8<br />BIAS<br />Systematicdeviationfromthetruththat<br />distortstheresultsofresearch<br />Occur anywhere within the research process<br />
  12. 12. 9<br />Interest association<br />CONFOUNDING<br />Outcome<br />Exposure<br />CA Colon<br />Junk Food<br />Confounder<br />Smoking <br />
  13. 13. 10<br />CONFOUNDING<br />The distortion of the apparent effect of an exposure on risk brought about by the association with other factors that can influence the outcome <br />e.g. effect of coffee drinking on myocardial infarction<br /> is measures as estimated relative risk of 1.8<br />The specific relative risk in non-smokers is 1.2<br />The specific relative risk in smokers is 2.7<br />
  14. 14. 11<br />Random error<br />A wrongresultsduetochance,<br /><ul><li>unknownsourcesofvariationbeingequally</li></ul>likelytodistortthefindingsineitherdirection<br />The effect of random error can be reduced by recruiting larger numbers or by adjustment for known confounders in the analysis<br />
  15. 15. 12<br />Study Designs<br />No comparison group<br />Descriptive<br />Naturalexposure<br />Observational<br />
  16. 16. 13<br />Descriptive Study <br />A study concerned with and designed to describe the existing distribution of interest outcomes, without regard to causal or other hypotheses<br />
  17. 17. 14<br />Example of descriptive study <br />The Epidemiological Study of Teenage Pregnancy<br />In Malawi, during 2000-2008<br />DISCUSSION<br />The Epidemiological Study of Incidence of Lung Cancer<br />In Thailand during 2000-2005, and major Risk Factors<br />
  18. 18. Random<br />Sample<br />Follow-up bias<br />-main outcome <br />-other interested outcomes <br />Structure of descriptive study<br />Population;<br />the group to be concluded by the study results<br />Selection bias<br />Cross-sectional OR Longitudinal<br />Measurement bias<br />
  19. 19. 16<br />Descriptive Study <br />Advantages<br /><ul><li> Cheap
  20. 20. Finding can be used to generate research hypothesis for further higher designs</li></ul>Limitation<br /><ul><li> Association found can not be infer directly to the population </li></li></ul><li>17<br />No comparison group<br />Descriptive<br />Naturalexposure<br />Observational<br />Type of Designs<br />Analytical<br />With comparison group<br />
  21. 21. 18<br />COHORT<br />CASE - CONTROL<br />CROSS-SECTIONAL<br />ANALYTICAL STUDY<br /> EXPOSURE<br />OUTCOME<br />PRESENT<br />FUTURE<br />PAST<br />
  22. 22. 19<br />With outcome<br />Without outcome<br />With outcome<br />Without outcome<br />Cohort<br />Selected for<br />study<br />Exposed group<br />Non-exposed group<br /> COHORT STUDY<br />
  23. 23. Having circulatory disease<br />No circulatory disease<br />Having circulatory disease<br />No circulatory disease<br />Pregnant women with hypertensive disease<br />Pregnant women during<br />1951-1970<br />1999<br />Pregnant women without hypertensive disease<br /> COHORT STUDY<br />20<br />
  24. 24. 21<br />Retrospective<br /> COHORT STUDY DESIGNS<br />Select groups in 2003<br />Trace<br />2028<br />1968 2003 <br />
  25. 25. 22<br />Prospective<br /> COHORT STUDY DESIGNS<br />Select groups in 2003<br />Follow<br />2028<br />1968 2003 <br />
  26. 26. 23<br />Prospective<br />Retrospective<br /> COHORT STUDY DESIGNS<br />Historical prospective<br />Select groups in 2003<br />Follow<br />Follow<br />2028<br />1968 2003 <br />
  27. 27. 24<br /> COHORT STUDY<br />ADVANTAGES<br /><ul><li> Prospective data collection
  28. 28. Temporality (time-sequence)
  29. 29. Allows for calculation of incidence outcomes in </li></ul> exposure and non-exposure individuals<br /><ul><li> May be used to study multiple outcomes
  30. 30. Efficient for studying rare exposures
  31. 31. Minimize recall bias</li></li></ul><li>25<br /> COHORT STUDY<br /> LIMITATIONS<br /><ul><li> Tend to be expensive (large sample size) </li></ul> and time consuming (long follow-up period)<br /><ul><li> Possibly having non-comparative group
  32. 32. Loss to follow-up
  33. 33. Ineffecient to study rare outcome</li></li></ul><li>26<br />Cautions when implementing a cohort study<br /><ul><li> Chance of outcome have to be occurred among </li></ul> comparative groups<br /><ul><li> Exposure and non-exposure groups are clearly </li></ul> different but all other factors be very similar <br /> ( to reduce selection bias)<br /><ul><li> Outcome must be measured by the same tool and </li></ul> procedure among the groups <br /><ul><li> Having a good plan for preventing lost to follow-up</li></li></ul><li>27<br />Plan for implementing a cohort study <br />Title:Passive Smokingandriskofcoronaryheartdiseaseinwomen: prospectivecohortstudy<br />BMJ 1998;317:1341–5<br />Objective:<br />Toexaminetherelationbetweenpassive smoking andriskofcoronaryheartdiseasein acohortofwomenfromtheALSPAC<br />Population: womenfrom 34 to 59 yearsofagewithoutpreviouslydiagnosedcoronaryheartdisease,stroke, orcanceratbaselinein 1980.They were classified to fourcategoriesforpassive smoking, included; almostnever, 1­3 timespermonthtoonceperweek, 2­4 timesperweek, and >5 timesperweek.These categories were represented 4 groups of exposure.<br />
  34. 34. 1 NOVEMBER 2003<br />Design 1-11-03<br />28<br /><ul><li>Themain outcome:</li></ul>Incidentcoronaryheartdisease, definedasnon­fatalmyocardialinfarctionorfatalcoronaryheartdiseaseoccurringafterthereturnofthe 1980 questionnairebutbefore 1 June 1994.<br /><ul><li>Measurement:</li></ul>Themedicalrecordsofwomenwhoreported a non­fatal<br />myocardialinfarctionwerereviewedbyphysicians<br />blindedtoselfreportedriskfactorstatus.Non­fatal<br />myocardialinfarctionwasconfirmedinaccordance<br />withthecriteriaoftheWorldHealthOrganisationplus<br />eitherdiagnosticelectrocardiographicchangesor<br />elevatedserumconcentrationsofcardiacenzymes.<br />
  35. 35. 29<br />Potentialconfoundingvariablesincluding <br />age,bodymassindex, hormonesfortreatingthemenopause, alcohol, multivitamin, andvitamin Esupplementswereupdatedeverytwoyears.<br />Aspirinusewasassessedin 1980, 1982, 1984, and 1988. Vigorousexercisewasassessedin 1980.<br />
  36. 36. 30<br />Statistical Analysis:<br />Therelativeriskwascomputedastheratein a specificcategoryofpassive smoking dividedbythatinthelowestcategory (almostnever),withadjustmentforageinfive­yearcategories.<br />Inmultivariateanalyses, intakeoftotalenergy, fat intake, andotherpotentialconfoundingvariableswere simultaneouslyincluded .<br />