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Chronic Disease In Malaysia



Research Methodology - Study Designs

Research Methodology - Study Designs

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Research Methodology - Study Designs

  1. 1. Basic Statistics (FK6163) Principles of Research Methodology Study Designs A presentation by Assc. Prof. Dr Azmi Mohd Tamil, Department of Community Health, Faculty of Medicine, Universiti Kebangsaan Malaysia
  2. 2. Research1. A systematic & organised scientific process to find answers to the questions.2. Getting specific answers to specific questions.3. Involves data collection, analysis & interpretation.
  3. 3. Research ProcessProblem selectionLiterature reviewFormulation of research objectivesSelection of variablesSelection of the appropriate studydesignSampling of populationData collectionAnalysis of dataPresentation of findings
  4. 4. Identifying the appropriate study design Research Methodology
  6. 6. Comparison between different designs
  7. 7. The study design differs from one another by;Intervention – present/absentTemporal sequence – when is the riskfactor and outcome measured;– At the same time– Risk factor before, outcome later– Outcome first, then risk factor (retrospectively)Sampling methods
  8. 8. Difference Between Study DesignsStudy Design Intervention Temporal Sequence Sampling Risk Factor andCross Sectional Absent Yes Outcome at same time. Outcome first, then riskCase Control Absent Matching factor (retrospectively). Risk Factor first, thenCohort Absent Maybe Outcome.Clinical/ Intervene, then measure Present RandomisationCommunity Trial Outcome.
  9. 9. SAMPLINGThe process of selecting study subjects froma larger populationextent to which research findings can begeneralised to a larger populationto save time, money, efficiency and safety.PROBABLITY SAMPLING - equal chance to bechosen ex. simple random, systematic, stratified,multistage, clusterNON-PROBABILITY SAMPLING - convenience,quota, purposive.
  10. 10. POPULATION TO CHOOSE FOR THE SURVEYSELECT REPRESENTATIVE POPULATION? sampling methods - simple random sampling (may not be practical in national study) - stratified random sampling (in hetero/ stratum) - multistage sampling (national-state- district-sub district-village) - cluster sampling
  11. 11. Which design is appropriate for my study?
  12. 12. How to study the problems or prove the hypothesis?Select appropriate study design - Descriptive - case report, case series, ecological correlation - cross-sectional / survey - case-control - cohort - intervention - clinical trial/ community trial
  13. 13. Questions that need to be answered ?distribution of blindness - descriptive ?correlation between import of fruits and visual acuity among the population - ecological correlation ?prevalence of blindness, cataract or poor vision - cross-sectional/survey ?association between vit A def. and blindness - case-control
  14. 14. Questions that need to be answered ?incidence and relative risk of radiation cataract among radiographers- cohort ?therapy/preventive methods useful or effective , daily vit A supplementation to prevent xeropthalmia - intervention
  15. 15. CROSS-SECTIONAL STUDYAlso known as Prevalence Study or Survey.
  16. 16. Cross-Sectional StudyMeasures the relationship of variablesin a defined population at oneparticular timeBoth risk factors (exposure) anddisease outcome are observed at thesame (point in) time in a sample (orthe entire population) of subjects.
  17. 17. Exposure & OutcomeExposure Outcome Time Confounders
  18. 18. Cross-Sectional StudyRisk Factor Outcome Time ConfoundersBoth Risk Factor & Outcome measured at the same time.
  19. 19. Cross-Sectional Study Risk Factor -Race Outcome-Diabetes Mellitus Disease + (14%) Indians (15%) Disease - (86%) Sample ratio Disease + (8%) Others (85%) Disease - (92%)Time Both Risk Factor & Outcome measured at the same time.
  20. 20. RESEARCH QUESTIONSWhat is the nature / magnitude of theproblem?Who is affected?How do the affected people behave?What do they know, believe, thinkabout the problem?We know very little about theproblems and its possible causes.
  21. 21. CROSS-SECTIONAL SURVEYMAY BE REPEATED - tomeasure changes over timeLARGE SURVEY - limitedvariablesSMALL SURVEY - unlimited
  23. 23. COMPARATIVE CROSS- SECTIONAL STUDYAN ANALYTICAL STUDYattempts to establish causes or riskfactors for certain problems e.g.– obesity and IGT– level of cholesterol and CHD– betel leaves and NIDDM– milk consumption and IDDM
  24. 24. Comparative Cross- Sectional StudyBoth risk factor(s) and outcome weremeasured at the same point in time inthe selected sample or population.The sample may have been selected torepresent the population being studied.The selection or sampling method maybe random or not-random (refer tosampling method notes).
  25. 25. COMPARATIVE CROSS- SECTIONAL DESIGN disease present factor present disease presentPOPULATION factor absent disease absent factor present disease absent factor absent
  26. 26. HOW TO COMPARE?PREVALENCE OF DISEASE INDIFFERENT SUBGROUP– Rate of DM among obese vs rate of DM among normal BMIPRESENCE OF VARIABLES (ORABSENCE) IN DISEASE VS NON-DISEASE– Rate of contact with pigs among those afflicted with Nipah virus against those free from the disease.
  27. 27. COMPARE RATES Disease Rate of disease TOTAL among the + -Exposure exposed + A B A+B = A/(A+B) - C D C+D Rate of disease among the non- TOTAL A+C B+D N exposed = C/(C+D) Disease Prevalence =(A+C)/N
  28. 28. ADVANTAGEScheaper, easier and fastercan study associationable to generalise findings to thelarger population prevalence – for planning, measure burdenof disease, identify high risk population.As a baseline for future cohort study
  29. 29. DISADVANTAGESCan show association only but NOTCAUSATION – no temporal sequencesurvivors problems – only those whostill survive are studied, may miss thecontribution of those that already diedfrom the disease.not suitable for rare diseases, or inremission etc.possible biases - selection,misclassification
  31. 31. CASE CONTROL STUDY - CONCEPTcomparison of group of diseasedperson (cases) with another group ofnon-diseased person (control) for pastexposure to a suspected cause of thedisease.arises because of hypothesis that therisk factor (exposure) causes thedisease
  32. 32. Case-Control Study Exposure Outcome Look back in time Time ConfoundersStarts with Outcome, then trace the retrospective exposure
  33. 33. Case-Control Study Outcome-Cataract Risk Factor-Diabetes Mellitus DM + (50%) Cataract Sample DM - (50%) ratio (1:1) DM + (8%) Normal vision DM - (92%)Time Past Starts with Outcome, then trace the retrospective exposure
  35. 35. CASE SELECTIONDetermine clear and reproducibledefinitions of the health problems to bestudied (avoid misclassification bias)source of cases All persons with the disease seen inparticular facility(ies) in a specified periodof time. All persons with the disease found ingeneral population.Incidence cases (newly diagnosed cases)preferred
  36. 36. CHOICE OF CONTROLSControls should ideally be selected from thesame population gave rise to casesSimilar to cases in regard to past potentialexposureFree from study diseaseIf controls are patient with other diseasesthen select only diseases that are not knownto have relationship with factors understudy.
  37. 37. MATCHING to take account for potentially confounding variables type of matching : • Frequency matching : selection of controls with the same proportionate distribution of the particular variable as the cases. (eg. age and sex) •Individual matching : pairing the controls with the cases on some common variables such as age, sex and ethnic group.• Matched variables cannot be evaluated
  38. 38. ASSESSMENT OF EXPOSURE Exposure should be assessed by the same method for both cases and controls blinding methods of assessment : • available records - hospital, vital, employment •interview •self-administered questionnaire •direct measurement• Comparability of the accuracy and completeness of data
  39. 39. UNMATCHED CASE- CONTROL STUDY OUTCOME CASE CONTROLRI Exposed a bSKFAC NotTO exposed c dR Analysed using Chi-Square & Odds Ratio = ad/bc
  40. 40. MATCHED PAIR CASE- CONTROL STUDY CASES Exposed Not exposedCO Exposed a bN (both pairs exposed) ( pairs of controls exposed)TR NotO exposed c dL (pairs of cases exposed) (both pairs not exposed) Analysed using McNemar and Odds Ratio = c / b
  41. 41. ADVANTAGESable to study rare diseasescan explore multiple exposuresrelatively inexpensivecan calculate Odds Ratiocan support causation but not prove iteasy to get cases
  42. 42. DISADVANTAGESAffected by biases such as selectionbias, information bias, recall bias.Temporal relationship may not beclear.Inefficient for rare exposureCan study only one outcome at a timeCannot measure prevalence orincidence.
  43. 43. COHORT STUDY
  44. 44. COHORT STUDYBASIC CONCEPT Group or groups of individuals are studied over time as to onset of new cases of disease and factors associated with the onset of disease. Synonyms : incidence study, longitudinal study, prospective study.
  45. 45. Cohort Study Exposure Outcome Look forward in time Time ConfoundersStarts with Risk Factor, then measure the future Outcome
  47. 47. Cohort Study Risk Factor-Weight Outcome-Diabetes Mellitus DM + (32%) OverweightFree Sample DM - (68%)from ratioDM (1:1) DM + (7%) Normal DM - (93%) Time Future Starts with Risk Factor, then measure the future Outcome
  48. 48. THE PURPOSE OF COHORT STUDYTo identify risk factors for diseaseto identify protective factors againstdiseaseto identify prognostic factors foroutcome of diseaseto describe the natural history of diseaseto determine the number of new cases ina population over time for :planning acute care servicesassessing effectiveness of preventivemeasures
  49. 49. TYPE OF COHORT STUDYPROSPECTIVE COHORT STUDY: the cohort assembled at the start of thestudy, followed over time (into thefuture) to determine the incidence ofdiseaseHISTORICAL COHORT STUDY:the cohort assembled in terms of aparticular exposure in the past and arefollowed through existing records intothe future.
  50. 50. CLASSICAL VS DYNAMIC COHORTCLASSICAL OR CASE-NONCASE- cohorts are counted by person contribution overtime, the denominator for incidence rate is population at risk.DYNAMIC OR POPULATION TIME cohorts are counted by person-time contribution overtime, the denominator for incidence density is person-time at risk
  51. 51. RecruitmentThose recruited must be free from thedisease of interest at the beginning ofthe study.Those with sub-clinical presentations ofthe disease may miss from beingexcluded. This is one of the challenges.
  52. 52. SELECTION OF COHORTSSOURCES :- geographically defined groups- special resource groups -doctors,nurses, factory workers etc.- special exposure group - expose toradioactive, asbestos, benzene, hazeCOMPARISON GROUPS :- similar in all respects except exposure
  53. 53. Cohort DefinitionBoth groups (E+ & E-) must have equalchance of being followed up.Types of cohort;– Representative – low exposed subjects– Enriched – high exposed subjects– Specific group – occupational, institutional etc.
  54. 54. ASSESSMENT OFEXPOSURE AND OUTCOMEINFORMATION ON EXPOSURE: records, cohort members, medical examination and measures of the environmentINFORMATION ON OUTCOME periodic reexamination surveillance of deaths, hospitalization, clinic visits
  55. 55. Follow-upKeep participation at > 90%Must have equal ability to detect disease in allsubjects and all groups, with standardmeasurementActive vs Passive follow-upVerbal AutopsyBlinding of the assessorAssess both primary and secondary outcomes
  56. 56. COHORT STUDY Relative risk (risk ratio)A measure of how many times more likelyare exposed persons to get the diseaserelative to non-exposedUseful for causative associationsSize of RR does not necessarily indicatemagnitude of incidence rates in exposedand non-exposed groupsCompares the relative contributions of riskfactors no matter how much of the diseaseexists
  57. 57. Cohort Study: Basic Steps Total population/sample No disease (a) Disease (b) No exposure (c) Exposure (d) ExcludeDisease (e) No disease (f) Disease (g) No disease (h) Relative risk = Ie/Ie = (g/d)/(e/c) ranges from zero (strong negative association) to infinity (strong positive association)
  58. 58. Relative Risk Cohort Study OUTCOME Disease + Disease -RI Exposed a bSKFAC NotTO exposed c dR Relative Risk = (a/(a+b))/(c/(c+d))
  59. 59. AdvantagesAble to show causationAble to measure riskMay represent populationIf the exposure occurs rarely, thencohort is a good way to study theoutcome.Can directly measure incidence
  60. 60. DisadvantagesHigh cost, longer time & relativelymore difficult to execute.Many subjects lost to follow-up.Control subjects may end up beingexposed i.e. start smokingNot suitable for rare diseasesBiases – more scrutiny of the exposedgroup.
  61. 61. Clinical Trials
  62. 62. CLINICAL TRIALAny prospective controlled assessment of :1. A treatment method2. Diagnostic technique3. Preventive measuresCharacteristicsPROSPECTIVE – cohort or group of patients,followed over a period of time, evaluation ofoutcome.CONTROLLED – 2 or more groups of patients. Allgroups are comparable to one another with respect toall factors relevant to the outcome
  63. 63. Clinical Trial Intervention Outcome Look forward in time Time ConfoundersStarts with Intervention, then measure the future Outcome
  64. 64. Clinical Trial Intervention Outcome-Improved? Improved (75%) Fluoxetine Sample No improvement (25%)Depressedpatients ratio (1:1) Improved (70%) Sertraline No improvement (30%) Time Future Starts with Intervention, then measure the future Outcome
  66. 66. EXPERIMENTAL STUDY C+ T+ C- Study EligiblePopulation Participants C+ Selection T- Randomisation C- Future
  67. 67. SELECTION OF SUBJECTSNumber, sourcesInclusion criteria : age range, sex, weight,diagnostic criteria, informed consent,cooperationExclusion: lack of inclusion criteria,pregnancy or lactation, drug allergy, diseaseseverity, other disorders, requirement ofother drugs, unresponsive cases, mentalstatus.
  68. 68. RANDOMISATIONMethod for inducing comparability betweengroupsEnsures that characteristics known orunknown did not influence the treatmentassignedTreatment given to the patient/next patientto enter the trial is determined purely bychance, not by any characteristics of thepatient
  69. 69. RANDOMISATIONAllows the computation of the probabilitythat the groups differ for both known andunknown characteristics.Does not guarantee perfect comparabilityBetter than any known procedureEach patient enter the trial has an equalchance of receiving which ever therapy
  70. 70. COMPARISON GROUPTo allow the evaluation of the outcomesof interest in a comparable group ofpatients who received a standard orbest available relevant alternativetreatmentThe effect of treatment are compared tothe effects of a control treatment
  71. 71. COMPARABILITYThe patients should not differ in anycharacteristics, known or unknown,relevant to the outcomes of interestother than the treatment employed.
  72. 72. Parallel vs Crossover Start BStart A B A A B B AEnd A B End B A
  73. 73. Crossover DesignDisease under study must be chronicand treatable but not curableDisease must be stable over course ofstudyUpon analysis, must consider; Period effect Carryover/residual effect
  74. 74. ADMINISTRATION OF STUDYInstitutional review – ethical committeeInformed consentReceipt, distribution and storage ofinvestigational suppliesInstructions to recordersInstructions to subjectsAdverse reaction reportingMonitoringReporting results
  75. 75. PROCEDUREAssignment of subjects to treatmentsInterview and examinationsMethods of assessmentLab. StudiesTreatment schedules: number of units pervisit, rules fo changing dosage, compliancechecksAdverse reactions: definition and grading,inquiry, management.Drops out: definition, handling andrecording, terminating and extending study
  76. 76. BLINDINGSingle blind : either the patient or thephysician knows the treatment whichhas been assignedDouble blind: neither the patients northe physician are aware of the treatmentassignedTriple blind: even the statistician notaware of the assignment.
  77. 77. FOLLOW-UP SCHEDULEThe schedule of visitsThe duration of follow-upMeasurement and procedures to beconducted at each visitsIn multi-centre trial, the methodologyof all measurements and proceduresshould be specified thoroughly.
  78. 78. EXPERIMENTAL STUDYADVANTAGES DISADVANTAGES the best design to Exposed to biases determine causal – selection, association and – attrition, evaluate program – compliance and performance – contamination biases. ethical implications
  79. 79. COMMUNITY TRIALS1. All prophylactic vaccines, such as those againstmeasles and rubella (german measles), diphtheria, andpolio, were tested on populations of children to prove theirefficacy in preventing the diseases.2. Prophylaxis with drugs such as penicillin to preventepisodes of rheumatic fever or isoniazide hydrochloride(INH) in the prevention of active tuberculosis.3. Antihypertensive drugs for the reduction of bloodpressure and prevention of complications such as stroke.They were proven effective in clinical trial experiments.4. Testing various forms of health service delivery, suchas comparing family practitioner services with physicianspecialty services.5. Health effects of radiation following the atom bombexplosions of 1945, the famine in Africa of 1974, of loss ofjobs in the recession of 1980.
  80. 80. TERIMA KASIH
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Research Methodology - Study Designs


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