To learn the common study designs To learn the hierarchy of study designs To learn the advantages and disadvantages of study designs To be able to select a study designs Introduction ID: 1044221
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1. Study Designs
2. ObjectivesTo learn the common study designs.To learn the hierarchy of study designs.To learn the advantages and disadvantages of study designs.To be able to select a study designs.
3. IntroductionInterested in Exposure, and/orEg. smoking, medicine, risk factors, etc.OutcomeEg. cancer, cure, disease, etc.ExposureOutcome
4. IntroductionObservational studiesInterventional studies
5. Observational StudiesEcological studiesCase reportCase seriesCrossed sectional studiesCase controlCohort study
6. 1. Ecological StudyFocuses on the comparison of groups or aggregate data, rather than individualsQuick, inexpensiveHelp in formulating hypothesisDisadvantagesInability to link exposure with disease (ecological fallacy)Inability to control for confounding
7. Ecological StudyEg. Per capita smoking in different countries and cancer rate per 100,000 adults
8. 2. Case ReportDocumenting rare / novel observation.May indicate a new link between exposure and outcome.DisadvantagesIt may occur by chanceSingle case
9. Case Report
10. Case ReportBMJ Case Reports 2014; doi:10.1136/bcr-2014-204986Green urine in a postoperative patientAn 85- year-old man underwent reversal of loop ileostomy. The integrity of the anastomosis was tested by an injection of methylene blue into the bowel lumen. Postoperatively the patient voided ‘green urine’ and alarmed the nursing staff and junior duty doctor. Routine microscopic examination and culture of urine revealed no abnormality. Liver function test and full blood count was also normal. This discolouration of urine resolved spontaneously in the next few days.
11. 3. Case SeriesSimilar with case report but observe more cases. To document potential link between an exposure and outcome.DisadvantagesIt may occur by chanceFew casesAbsence of control
12. Case SeriesAccording to previous example, how would you imagine a case series to be?Collection of case reports, reporting methylene blue causing green urine.Eg. 10 case reports, and compile them into a case series.
13. 4. Cross-sectional StudyData collection on exposure and outcome are conducted at the same time.Snap shot of the studied population.Descriptive: Prevalence of cervical cancerAnalytical: Association of risk factors (ie. age, SES) and presence of cervical cancerCheap and quick.Able to study multiple risk factors and outcomes at the same time.No loss to follow-up
14. Cross-sectional StudyDisadvantageUnable to determine causality (cause and effect)Not suitable for rare exposureUnable to establish temporal relationship (ie. alcohol consumption and depression)ExposureOutcome
15. 5. Case Control StudyRelatively cheap and quickCan investigate many exposuresSuitable for rare diseasesNo loss to follow-upExposureOutcomeStudy start at outcome
16. ExposedDiseaseStudy start at outcomeNon DiseaseNon ExposedExposedNon exposed
17. Case Control StudyDisadvantageSelection biasInformation biasNot suitable for rare exposures
18. 6. Cohort StudyUseful for rare exposureStudy multiple outcomes with single exposureTemporal relationship can be establishedRisk of measurement bias can be minimizedExposureOutcomeStudy start at exposure
19. DiseaseExposedStudy start at exposureNon exposedNon diseaseDiseaseNon diseaseFollow up
20. Cohort StudyDisadvantages:Not suitable for rare diseasesExpensiveTime consumingLoss to follow-up bias problem
21. Observational StudiesCase reportCase seriesEcological studiesCrossed sectional studiesCase controlCohort study
22. Qualitative StudiesExploratory, Flexible, ComplexAuthors and world perspectiveCommon categories:PhenomenologyGrounded theoryEthnographyCase study
23. Qualitative StudiesCommon methodology:InterviewIndividualFocus groupSemi-structured, structuredObservationIndividual GroupLocationDocument analysis
24. Qualitative StudiesHow has the meaning and practice of informed consent in research changed over the last 35 years? Miller T and Boulton M (2007) ‘Changing constructions of informed consent: Qualitative research and complex social worlds’ Social Science and Medicine 65 (11) 2199-2211.‘Factors that help injecting drug users to access and benefit from services: A qualitative study’ Substance Abuse Treatment, Prevention and Policy 2 (31)
25. IntroductionObservational studiesInterventional studies
26. Interventional StudiesRandomized controlled trialsTrue experimentRandomizationConfounder distribution Minimize biasBlindingControlled
27. Interventional StudiesRandomization (equal chance)Toss of coinComputer generated random numberMs ExcelSTATASPSSIVRS
28. Interventional StudiesBlinding Single / DoubleParticipant / InvestigatorConcealment of randomizationDouble dummyAssessor and applicator
29. CuredNew treatmentStudy start at exposureStandard treatmentNot curedCuredNot curedPopulationRandomizationoutcome
30. Interventional StudiesDisadvantagesEthical issuesExpensiveTime consumingNeed strong justification
31. Hierarchy of Study DesignsRCTsCase control studiesCross sectional studiesCase studiesIdeas, expert opinions, editorialsAnecdotalCohort studiesSystematic review and meta analysis of RCTsLevel of evidence
32. FeaturesECOLOGICALEXPERIMENTALCOHORTCASE CONTROLCROSS SECTIONALStudy TypeDescriptiveExperimentalObservationalObservationalObservationalFeaturesAggregate measuresControlled exposure by experimenterE/not E known for all participants – Followed up over a long time periodCase chosen – incident or prevalent and then assessed for study factorControls often matchedOutcome and study factor studied simultaneously SamplingNone – measures entire populations eg. countriesOften convenient samples (eg. hospital settings)Diverse, largePrevalent or incident cases Control – population controls preferredIdeally a random sample of the target populationDirectionalityNon-directionalAlways forwardAlways forwardBackward (incident) Non (prevalent)Non or backwardUsed whenEstablishing association in summary statisticsFor therapeutic or preventive assessmentExposure rare, Outcome frequentRetrospective for rare disease, long inductionFrequent exposure, Rare outcomesOutcome and exposure frequent, Study factor not changing over time, Incidence can be established elsewhere.
33. FeaturesECOLOGICALEXPERIMENTALCOHORTCASE CONTROLCROSS SECTIONALDetermining CausalityNot possible ++++++Not possibleStrength of studyLow as not at individual levelMOST POWERFULMost powerful observational studyNext most powerful observational studyWeakest observational study but useful for prevalence.ProblemsEcological fallacyVolunteerism, complianceLoss of participantsDefined by outcome, unable to look at multiple effects of study factorCan’t use for rare outcomes, diseases with short durations.CostLow, if data availableExpensiveHigh and time consumingLess in time and money cf cohortLowMajor Potential BiasInformation biasSelection bias, Information biasSelection bias – dropoutsInformation bias – Recall if retrospectiveSelection bias – matching controlsInformation bias – Recall bias, poor recordsSelection biasInformation – Recall biasControlling for confounding Randomisation – Check it worked Collect data on all potential confoundersCollect data on all potential confoundersMatching to control for strong confounders, collect data on all potential confoundersCollect data on all potential confounders.
34. How do we select?Research questionsEthical considerationsResources
35. Case Scenario 1Wilm’s tumor is a kidney cancer that affects children very early in life. It is more common in West Africa than most parts of the world. The reasons for this are obscure. The fact that most affected children have the disease at birth, or soon after, suggests that the cause of the cancer may act in utero.You wish to design a study to generate hypotheses about the possible exposures in utero that could lead to Wilm’s tumor.
36. Case Scenario 2Vitamin E is known as an intracellular antioxidant that might protect against cancer, but studies on animals and humans have yielded somewhat conflicting results. Select a study design to examine the effect of vitamin E on the risk of cancer.
37. Case Scenario 3An epidemiology graduate student finds evidence in the literature that childhood sunlight exposure may affect adult breast cancer risk. Select a study design to explore this hypothesis
38. Case StudyAn exploratory study of the effect of mahjong on the cognitive functioning of persons with dementiaSheung-Tak Cheng, Alfred C. M. Chan and Edwin C. S. YuINTERNATIONAL JOURNAL OF GERIATRIC PSYCHIATRYInt J Geriatr Psychiatry 2006; 21: 611–617.
39. ReferencesBonita R, Beaglehole R, Kjellström T. Basic Epidemiology 2 ed. Geneva: World Health Organization; 2006.Rothman KJ, Greenland S. Causation and causal inference in epidemiology. American journal of public health 2005;95 Suppl 1:S144.Gordis L., Epidemiology 4th ed. Philadelphia: Saunders Elsevier; 2009.Mason J (2002) Qualitative Researching (2nd edn) London: Sage Publications.
40. AcknowledgmentAcknowledgment to Chew CK for preparation of the core contents of this presentation.
41. Dear CK,I’m just summarising some suggestions given by the other speakers regarding your topic on study design. Also, as the actual GPCR course has increased to 2.5 days, the slot for Study design has been increased to 1.5 hours. So kindly amend the contents for the 1.5 hours of lecture ya. The following are the suggestions of information to be added into your powerpoint:1. To state on randomisation method: eg: toss of coin if only 2 study groups, using sealed envelope, generate of random tables. Etc2. To state on how to do blinding3. To include study design for Qualitative studies, methods and pros and cons of different methods: ie: face-to-face interview, focus group etc4. To provide a case study using a published article and further discuss or critique on the study design. The dateline for submission of new slides is by 10/11/14(Monday). Also, please add in an acknowledgement slide for yourself in the powerpoint. Do send it to lai at laiwh@crc.gov.my