Epidemiological studies


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  • Ask the learners to define Epidemiology
  • Health related states include disease and non-disease states. Example of non-disease states – injury, substance use, suicide
  • Ask learners to explain the uses of epidemioloy
  • Epidemiological studies

    2. 2. OUTLINE Classification of studies Study Designs and analysis Choice of study design 2
    4. 4. CLASSIFICATION Various ways BUT, two major classes  Non-Interventional  Interventional 4
    5. 5. Non-Intervention studies Researcher do not manipulate situations/objects  Just describes or analyses situations/objects 5
    6. 6. Intervention studies Researcher manipulates situations/objects then describes or analyses the outcome 6
    8. 8. Non-Intervention studies 8
    9. 9. Types of Non- Interventional studies Exploratory Descriptive Analytical 9
    10. 10. Exploratory studies Small scale studies Gathers information about unfamiliar phenomenon Results gives insight to a problem before a large scale study is designed 10
    11. 11. Descriptive studies Only describe phenomena: e.g. Person, Place, Time No analysis of determinants/association  E.g. Cross-sectional descriptive 11
    12. 12. Cross-sectional descriptive Aim at just describing phenomenon Done at one point in time – hence Cross-sectional  E.g. Prevalence studies, KAPB studies 12
    13. 13. Analytical studies Describe phenomena  And Analyze relationship between phenomena and other variables (determinants/association).  Examples:  Cross-sectional comparative  Cohort study  Case-control study 13
    14. 14. Cross-sectional comparative study Aim at describing phenomenon and compare groups or determine factors influencing the phenomenon Done at one point in time Measurement of exposure and effect are done at the same time 14
    15. 15. Advantages and Disadvantagesof Cross-sectional studiesAdvantages Disadvantages Quick and cheap  Not possible to determine Can elucidate various if the exposure preceded exposures, as first the outcome (temporal step in investigating relationship) cause  Bias** Repeated measures can depict trend Data useful in assessing health care needs 15
    16. 16. Cohort studies 16
    17. 17. Cohort study (“Prospective, “Followup” study) Aim at determining risk factors for diseases/outcome At the start identify two groups  With exposure to a risk factor (exposed)  Without exposure (no-n exposed) Both groups have not developed the disease/outcome at the start Follow over time At the end, analyse disease/outcome occurrence in both groups and compare 17
    18. 18. Design of Cohort study - I Time Inquiry Disease Start Exposed No diseasePopulation Non-diseased people Non-exposed Disease No disease 18
    19. 19. Design of Cohort study - II Exposed and non-exposed groups must be comparable in all factors that may be related to the disease except for the exposure Need to get complete and accurate information about exposure and outcome for all individuals 19
    20. 20. Analysis of Cohort studies Compare incidences of disease among exposed to non-exposed group  Cumulative incidence (Calculate Relative Risk) (commonly)  Incidence rate (Calculate Incidence rate ratio), - when person time of follow up is known 20
    21. 21. Advantages & Disadvantages Advantages  Disadvantages  Allows direct  Time consuming, measurement of expensive incidence of disease  Inefficient in  Multiple effects of evaluating rare single exposure can be diseases examined  Loss of follow up affect  Can elucidate temporal validity of results relationship between exposure and disease  Is of value when exposure is rare  Minimize bias in ascertainment of exposure 21
    22. 22. Case – control studies 22
    23. 23. Case –control study(“Retrospective” study) Aim at determining risk factors for diseases/outcome At the start identify two groups  With disease/outcome (Cases)  Without disease/outcome (Controls) History of exposure to risk factor is inquired At the end, analyse exposures to a risk factor in both groups and compare 23
    24. 24. Design of Case-control study - I Time Start Inquiry Exposed Cases Non exposed Population Exposed Controls Non expose 24
    25. 25. Design of Case-control study - II Controls should be representative of the population from which the cases are recruited Cases and controls must be comparable in all factors that may be related to the disease except for presence of disease Controls can be chosen to match cases for certain important variables such as age, sex, etc = Matched Case-control design. If matching not done = Un- matched case-control design (more common) Need to get complete and accurate information about exposure for all individuals Control: Case ratio? Consider cost, availability of cases Usually ratio of 1:1 up to 4:1, beyond that no added advantage for power of the study 25
    26. 26. Analysis of Case-control studies Compare Exposure of disease among Cases to Controls  Calculate Odds Ratio 26
    27. 27. Advantages & Disadvantages Advantages  Disadvantages  Relatively quick  Inefficient in and inexpensive evaluating rare  Suitable for rare exposures diseases  Temporal  Can evaluate relationship effect of multiple between exposure exposures and disease difficult  Is of value for to ascertain diseases with long  Prone to recall bias latent periods 27
    28. 28. Intervention studies 28
    29. 29. Intervention studiesTwo main types: Experimental (Classical experiment) Quasi-experimental 29
    30. 30. Characteristics of Experimental studies  Manipulation  Something is done to one group (experimental group)  Presence of Control group (no manipulation done)  Randomization (assignment of individuals to experimental or control groups is done randomly)  Example: Randomized Controlled Trials (RCT) – “Gold standard” 30
    31. 31. Characteristics of Quasi-Experimentalstudies Manipulation Control group or Randomization missing  Example: Community trials 31
    32. 32. Design of Randomized controlled trial - I Exp. group Follow up & Study AnalysisGeneral pop Randomization PX Control group 32
    33. 33. Design of Randomized controlled trial - II Randomization ensures that chance alone determines which individuals become experimental group and which ones become control group  Thus, making the groups comparable in most aspects that may be related to the outcome Design provide strong evidence of the effect of the intervention – “Gold standard” Study participants are blinded about the intervention (Single blind) Sometimes both Study participants and investigators are blind about the intervention (Double-blind) 33
    34. 34. Ethical Considerations in Experimental studies Carried out only if:  Evidence suggest intervention is beneficial, but uncertain of effect  No serious adverse effect to the intervention group  Informed consent to participate 34
    35. 35. Analysis of Intervention studies Comparison of outcome of interest in experimental and control groups Comparison of baseline characteristics of experimental and control groups 35
    36. 36. Choosing a study designConsiderations: Ethical issues – minimal ethical concerns Resources and administrative issues Validity and reliability of results Nature of topic 36