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Study designs, Epidemiological study design, Types of studies

Study design, Epidemiological study designA study design is a specific plan or protocol
for conducting the study, which allows the investigator to translate the conceptual hypothesis into an operational one.

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Study designs, Epidemiological study design, Types of studies

  1. 1. STUDY DESIGNS - An Overview Dr Lipilekha Patnaik professor, Community Medicine Institute of Medical Sciences & SUM Hospital, Siksha ‘O’ Anusandhan deemed to be University Bhubaneswar, ODISHA, INDIA E mail– drlipilekha@yahoo.co.in 1
  2. 2. Session Outline Study designs and its types Observational and Interventional studies Uses of different studies Systematic review and metaanalysis Hierarchy of study designs in research An introduction to Qualitative study Ideal study design for different situations 2
  3. 3. Study Design A study design is a specific plan or protocol for conducting the study, which allows the investigator to translate the conceptual hypothesis into an operational one. 3
  4. 4. TYPES QUANTITATIVE QUALITATIVE 4
  5. 5. Quantitative vs Qualitative vQuantitative research is used to quantify the problem by way of generating numerical data which can be transformed into useable statistics. It can generalize results from sample to population. vQualitative research is exploratory research. It is used to gain an understanding of underlying reasons, opinions etc. and provides insight into the problem. 5
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  7. 7. Types of epidemiological studies Types of studies Alternative name Unit of study OBSERVATIONALSTUDIES ◦ Descriptive studies – Case report, case series Individuals ◦ Cross sectional surveys ◦ Analytical studies ◦ Ecological Correlation Populations ◦ Cross-sectional Prevalence Individuals ◦ Case-control Case-reference Individuals ◦ Cohort Follow-up Individuals EXPERIMENTALSTUDIES (Intervention Studies) ◦ Randomized control trials Clinical Trials Patients ◦ Field trials Healthy People ◦ Community trial Community studies Communities 7
  8. 8. DESCRIPTIVE STUDIES ØDescriptive study is the first phase of epidemiological investigation. ØObserving the distribution of disease or health related events in human population. ØIdentify the characteristics with which the disease is associated. ØBasically 3 questions are asked when, where and who i.e. Time, place and person distribution. 8
  9. 9. Case reports Case series Population studies (Cross sectional surveys) 9
  10. 10. Case Reports ØDetailed presentation of a single case. ØGenerally report a new or unique finding üe.g. previous undescribed disease üe.g. unexpected link between diseases üe.g. unexpected new therapeutic effect üe.g. adverse events 10
  11. 11. Case Series ØExperience of a group of patients with a similar diagnosis ØCases may be identified from a single or multiple sources ØGenerally report on new/unique condition 11
  12. 12. Cond. ØAdvantages •Useful for hypothesis generation •Informative for very rare disease with few established risk factors ØDisadvantages •Cannot study cause and effect relationships •Cannot assess disease frequency 12
  13. 13. Case Report Case Series One case of unusual findings Multiple cases of findings 13
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  15. 15. Uses Hypothesis generation Suggesting associations 15
  16. 16. ANALYTICAL STUDIES Ecological study Cross-sectional Case-control Cohort 16
  17. 17. Ecological Study žIt is not easy to establish links between environmentalexposures and health outcomes using individuallevel data. žEcological study designs provide one way of avoiding these difficulties and studying the effects of environmentalexposures on different health outcomes. žEcological studies look for associations between the occurrenceof disease and exposure to known or suspected causes. žHowever, the unit of analysis is not an individualbut a population / a group of persons 17
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  19. 19. Cross-sectional Study Data collected at a single point in time An “observational” design that surveys exposures and disease status at a single point in time (a cross-section of the population) Describes associations Prevalence 19 A “Snapshot”
  20. 20. 20 time Study only exists at this point in time Study population No Disease Disease factor present factor absent factor present factor absent
  21. 21. Sample of Population Playing outdoor games regularly Not playing outdoor games Prevalence of Overweight/ obesity Prevalence of Overweight/ obesity Time Frame = Present 21 Defined Population of school going adolescents Example
  22. 22. Why we do cross-sectional study? ØTo assess the burden of disease in a population and to assess the need for health services. ØTo compare the prevalence of disease in different populations. ØTo examine trends in disease prevalence or severity over time. ØTo find out association 22
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  25. 25. Case-Control Studies §Start with people who have disease (Cases) §Match them with controls that do not have disease §Look back and assess exposures 25
  26. 26. Other Name Retrospective Study Unit of Study Cases/Control Study QuestionWhat has happened ? Direction of Inquiry= F O Study Design 26
  27. 27. 27 Study population Cases (disease) Controls (no disease) factor present factor absent factor present factor absent present past time Study begins here
  28. 28. 28 Obese adolescents Normal adolescents PresentPast No Outdoor games No Outdoor games Regular outdoor games Regular outdoor games Cases Controls Example
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  30. 30. Cohort Study Cohort is defined a group of people who share a common characteristic or experience within a defined time period (age, occupation, exposure) Birth cohort, exposure cohort 30
  31. 31. Begin with disease-free individuals Classify patients as exposed/unexposed Record outcomes in both groups Compare outcomes using relative risk 31
  32. 32. Other Name Prospective Study / Follow-up Study/Incidence Study Unit of Study Individual Study Question What is happening ? Directionof Inquiry F O Study Design 32
  33. 33. 33 time Study begins here Study population free of disease Factor present Factor absent disease no disease disease no disease present future
  34. 34. Example 34 Not playing outdoor games Playing outdoor games regularly Not obese Obesity Obesity Not obese Present Future Cohort of School going adolescents
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  36. 36. EXPERIMENTAL STUDIES 1. Experimental studies are similar in approach to cohort studies excepting that the study condition are under direct control of the investigator. 2. There is some action, intervention or manipulation which are deliberate. AIM OF EXPERIMENTAL STUDY 1. To provide scientific proof of aetiological factor. 2. To provide a method of measuring the effectiveness and efficiency of health services for the prevention control and treatment of diseases. TYPES OF EXPERIMENTAL STUDIES 1. Animal study 2. Human study 36
  37. 37. Types 1. Randomised controlled trials 2. Non-randomised trials. 37
  38. 38. Other Name Intervention Study Objective To know the effect of intervention Unit of Study Individual meeting entry criteria Study Question What is happening after intervention in both groups ? Direction of Inquiry I E Study Design (Intervention with Standard of care or placebo) 38
  39. 39. Experimental Design 39 time Study begins here (baseline point) Study population Intervention Control outcome no outcome outcome no outcome baseline future RANDOMIZATION
  40. 40. Participants are allocated in to two groups. 1) study group : To receive preventive and therapeutic manoeuvres. 2) control group : Not to receive any intervention or to receive standard of care. 40 Randomisation
  41. 41. 41 time Study begins here obese students Intervention (Regular exercise &Outdoor games) Control Decrease BMI No change of BMI Decrease BMI No change of BMI Obese students Future (After 2 years) RANDOMIZATION
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  43. 43. Different studies have different uses Objective Type of study Prevalence Cross-sectional Incidence Cohort Causal association Cohort Case-control Prognosis Cohort Natural history of disease Cohort Treatment effect Randomised Controlled Trial 43
  44. 44. Did the investigator assign exposure? Experimental Study Observational Study Yes No Random Allocation? Comparison Group? Yes Yes No No Analytical Study Descriptive Study Randomized Control trial Non- Randomized Control trial Direction? Exposure Outcome Exposure and outcome at the same time Cohort Study Case Control Study Cross- Sectional Study Exposure Outcome 44
  45. 45. Systematic Review “A review that is conducted according to clearly stated, scientific research methods, and is designed to minimize biases and errors inherent to traditional, narrative reviews.” Margaliot, Zvi, Kevin C. Chung. Systematic Reviews: A Primer for Plastic Surgery Research. PRS Journal. 120/7 (2007) 45
  46. 46. Meta analysis ØMeta-analysis is a statistical analysis of a collection of studies. ØMeta-analysis methods focus on contrasting and comparing results from different studies in anticipation of identifying consistent patterns and sources of disagreements among these results. Ø“While all meta-analyses are based on systematic review of literature, not all systematic reviews necessarily include meta- analysis.” 46
  47. 47. Hierarchy of Study Design 47
  48. 48. QUALITATIVE RESEARCH Qualitative research can provide insight into the priblem which is not possible with purely quantitative data • A means for exploring and understanding the meaning individuals or groups ascribe to social or human problems • Study human behavior and social world Help us to understand the world in which we live and why things are the way they are 48
  49. 49. Qualitative research answer questions on: ◦Why people behave the way they do ◦How opinions and attitudes are formed ◦How people are affected by the events that go on around them ◦How and why cultures have developed ◦The difference between social groups 49
  50. 50. Which is the ideal study design? §A rare case of Dermatomyositis came to the hospital – Case report §Prevalence of Hypertension among adolescents in Bhubaneswar city – Cross sectional §To find out the association of bottle feeding with the incidence of diarrhea – Cohort §Association of Smoking and MI – Case Control §Safety and efficacy of Malaria vaccine – RCT §To explore factors of nonuse of contraceptives in a tribal community – Qualitative study 50
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