際際滷

際際滷Share a Scribd company logo

Epidemiological Designs.ppt

Download as PPT, PDF
R
reHANatabbasUm

This document discusses epidemiologic study designs. It begins by defining epidemiology and outlining the objectives of epidemiology. The document then explains the hierarchy of epidemiologic designs, including observational studies like case reports, case series, cross-sectional studies, and analytical studies like case-control and cohort studies. For each study design, the document provides examples and discusses their strengths and limitations for investigating disease determinants and establishing causality. It concludes by noting experimental studies allow investigators to determine and control interventions to evaluate preventive and therapeutic measures.

1 of 44
Download to read offline
Epidemiological Designs.ppt
2 Epidemiologic Study Designs Ms. Hajra Sarwar Assistant Professor LSN UOL Subject Code:NUR50105
3 Session Objectives By the end of this session, the Students will be able to: Define the term Epidemiology State the major objectives of Epidemiology Explain the hierarchy of epidemiological designs Identify the strengths & limitations of certain epidemiological designs
4 Epidemiology It is a study of distribution and determinants of health related states or events in a specified population and the application of this study to control health problems. (Stephenson & Babiker 2010),
5 Objectives of Epidemiology Identify the etiology or the cause of a disease and the risk factors Determine the extent of disease found in the community Study the natural history and prognosis of disease
6 Cont Evaluate the new preventive and therapeutic measures and new modes of health care delivery Provide the foundation for developing public policy and regulatory decisions relating to environmental problems
7 Types of Epidemiological studies Observational Interventional / Experimental -Investigator observes the course of a disease or the relation between the risk factor & outcome but does not intervene -Investigator attempts to prevent or change the course of a disease. -Are used to evaluate preventive and therapeutic interventions, can provide strong evidence of causality.
8 a) Descriptive studies: Examine patterns of disease (Concerned with describing the general characteristics of the distribution of a disease Particularly in relation to time, place and person) b) Analytical studies Studies of suspected causes of diseases (Examines the determinants of the health outcomes) OBSERVATIONAL:
9 Cont Experimental studies: Compare treatment modalities (RCTs)
10 10 Epidemiology studies Observational Descriptive Case report Case series Cross sectional Ecological Analytical Case control Cohort studies Cross sectional Experimental
11 Case Reports A case report is the description of a single case, typically describing the manifestations, clinical course and prognosis of that case and how it was managed. Describe rare clinical events or unusual manifestations of disease. Based on the experience of one patient only Example: In 1961, a published case report of a 40 year-old women who developed pulmonary embolism after beginning use oral contraceptive
12 Case Series An individual case report that has been expanded to include a number of patients with a given disease Often used to delineate the clinical picture of a disease Example: In Los Angeles, five young homosexuals men, previously healthy, were diagnosed with pneumocyst cariini pneumonia in a 6-month period
13 Strengths and limitation Strengths Generate hypothesis for further studies First form of publication Fast and inexpensive Limitation Most important limitation: absence of a comparison group No genaralizability Very weak to generate causal relationships
14 Cross-sectional study Often interest is to describe frequency and pattern of either disease or health-related outcome occurrence Usually data collected in a survey form Exposure and disease status are assessed simultaneously in a well-defined population
15 Prevalence Proportion of individuals in a population with disease at a specific point of time Provides estimate of the probability or risk at one will be ill at a point in time Provides an idea of how severe a problem may be Useful for planning health services (facilities, staff)
16 # of existing cases of disease P = X 100 Total population at risk Formula for Prevalence
17 Cross-Sectional Study Example: Hypothesis: Obesity is a risk factor for knee osteoarthritis Sample: 100 women living in Iqbal town Lahore
18 Advantages Quick, easy, and cheap Can study multiple exposures and disease outcomes simultaneously Good for describing the magnitude and distribution of health problems
19 Disadvantages Mixes prevalent and incident cases Cannot determine the temporal association
20 ? Chicken or egg dilemma do not know whether the exposure preceded disease, or was a consequence of disease development. OR
21 Ecological Study An ecological study focuses on groups of people (rather than individuals) as the units of analysis Uses data from entire populations to compare disease frequencies between different groups during the same period of time or in the same population at different point in time
22 Cont The variables include measurements taken at the group level e.g. infant mortality rates of different countries A common type of ecological study design involves comparison of treatment patterns and outcomes of patients living in different geographical regions or countries; such studies attempt to make inferences about the quality of care provided by the respective healthcare systems.
23 Yearly mortality vs. antibiotics
24 Analytical Epidemiology Analytical Epidemiology Analytical Cross Sectional Studies Case Control Studies Cohort Studies
25 Population Cases Controls Exposed Case-Control Studies Not exposed Exposed Not exposed
26 Case-Control Study - Aims to identify factors that may contribute to an outcome. In this type of study, subjects are selected based on the outcome variable; subjects who have the condition (cases) are compared with the subjects who do not have the condition (controls). Looking back in the time, the cases and controls are compared with regard to exposure. (Noordzij, Dekker,Zoccali & Jager, 2009; 7 Lu, 2009)
27 Strengths Cheap, easy and quick studies - Multiple exposures can be examined - Rare diseases and diseases with long latency can be studied -Hypothesis generating
28 Limitations Case and control selection troublesome -Subject to bias (selection, recall, misclassification) -- Temporal relationship is not clear -- some potential to generate causal relationship
29 Proportions Exposed: Cases Exposed = a / a+c Controls Exposed = b / b+d
30 The Measure of Association in a Case- control Study Is the Odds Ratio d c b a D E D E OR = Odds of exposure among diseased Odds of exposure among non-diseased OR = a / c = a d b / d b c =
31 OR > 1.0 (Positive Association) The odds of exposure among cases is higher than the odds of exposure among controls. OR = 1.0 (No Association) The cases are equally likely to have the exposure than the controls. OR < 1 (Negative Association) the odds of exposure among cases is less than the odds of exposure among controls. Interpretation
32 Calculation of the OR in Case-control Studies Example: A Case-Control Study of Bladder Cancer Cases Control Smokers 112 176 Non-smokers 88 224 Total 200 400 thus, OR = ad/bc = (112 x 224) / (176 x 88) =1.6 Bladder cancer cases were likely to have smoked 1.6 times more than controls.
33 Population People without disease Exposed Not exposed Disease No disease Disease No disease Cohort Studies
34 In a cohort study, an investigator defines a study population consisting of subjects who are free of the outcome of interest. This study design aims to determine which factors are associated with the development of this outcome. Depending upon the exposure status at the start of the study, subjects are classified as exposed or unexposed. Thereafter the subjects are followed over time to see who develops the outcome and who will not.
35 ineligible no participation deep chest SSI no deep chest SSI participation obese no participation deep chest SSI no deep chest SSI participation not obese CABG surgery performed at BJC hospitals during 1999 CABG patients Cohort Study
36 Relative Risk Measure of association between incidence of disease and factor being investigated Ratio of incidence rate for persons exposed to incidence rate for those not exposed Incidence rate among exposed RR = Incidence rate among unexposed Estimate of magnitude of association between exposure and disease
37 Incidence rate Incidence among exposed = a/a+b Incidence among non-exposed = c/c+d
38 Incidence rate among exposed RR = Incidence rate among unexposed Formula for relative risk: a / (a + b) RR = c / (c+ d)
39 RR > 1.0 (Positive Association) Risk is higher in exposed as compared to non exposed. RR = 1.0 (No Association) The risk is equal in the two groups. RR < 1 (Negative Association) The risk in the exposed is lesser than the non exposed. Interpretation
40 Cohort Studies Advantages & disadvantages: Can ascertain multiple outcome of single exposure High generalizability Hypothesis generating Can establish population-based incidence Accurate relative risk (risk ratio) estimation
41 Continue Temporal relationship can be inferred (prospective design) Magnitude of a risk factors effect can be quantified Multiple outcomes can be studied (smoking > lung cancer, COPD, larynx cancer) Time consuming and costly Loss to follow up ( participants can leave in between)
42 Epidemiologic Study Designs Grimes & Schulz, 2002 (www)
43
44 Experimental Study Defined A study in which the investigators determine and control the conditions of the experiment: Participants are randomly assigned to groups that experience carefully controlled interventions manipulated by the experimenter allowing causal inference about the effects of the interventions under investigation

More Related Content

Epidemiological Designs.ppt

  • 2. 2 Epidemiologic Study Designs Ms. Hajra Sarwar Assistant Professor LSN UOL Subject Code:NUR50105
  • 3. 3 Session Objectives By the end of this session, the Students will be able to: Define the term Epidemiology State the major objectives of Epidemiology Explain the hierarchy of epidemiological designs Identify the strengths & limitations of certain epidemiological designs
  • 4. 4 Epidemiology It is a study of distribution and determinants of health related states or events in a specified population and the application of this study to control health problems. (Stephenson & Babiker 2010),
  • 5. 5 Objectives of Epidemiology Identify the etiology or the cause of a disease and the risk factors Determine the extent of disease found in the community Study the natural history and prognosis of disease
  • 6. 6 Cont Evaluate the new preventive and therapeutic measures and new modes of health care delivery Provide the foundation for developing public policy and regulatory decisions relating to environmental problems
  • 7. 7 Types of Epidemiological studies Observational Interventional / Experimental -Investigator observes the course of a disease or the relation between the risk factor & outcome but does not intervene -Investigator attempts to prevent or change the course of a disease. -Are used to evaluate preventive and therapeutic interventions, can provide strong evidence of causality.
  • 8. 8 a) Descriptive studies: Examine patterns of disease (Concerned with describing the general characteristics of the distribution of a disease Particularly in relation to time, place and person) b) Analytical studies Studies of suspected causes of diseases (Examines the determinants of the health outcomes) OBSERVATIONAL:
  • 9. 9 Cont Experimental studies: Compare treatment modalities (RCTs)
  • 10. 10 10 Epidemiology studies Observational Descriptive Case report Case series Cross sectional Ecological Analytical Case control Cohort studies Cross sectional Experimental
  • 11. 11 Case Reports A case report is the description of a single case, typically describing the manifestations, clinical course and prognosis of that case and how it was managed. Describe rare clinical events or unusual manifestations of disease. Based on the experience of one patient only Example: In 1961, a published case report of a 40 year-old women who developed pulmonary embolism after beginning use oral contraceptive
  • 12. 12 Case Series An individual case report that has been expanded to include a number of patients with a given disease Often used to delineate the clinical picture of a disease Example: In Los Angeles, five young homosexuals men, previously healthy, were diagnosed with pneumocyst cariini pneumonia in a 6-month period
  • 13. 13 Strengths and limitation Strengths Generate hypothesis for further studies First form of publication Fast and inexpensive Limitation Most important limitation: absence of a comparison group No genaralizability Very weak to generate causal relationships
  • 14. 14 Cross-sectional study Often interest is to describe frequency and pattern of either disease or health-related outcome occurrence Usually data collected in a survey form Exposure and disease status are assessed simultaneously in a well-defined population
  • 15. 15 Prevalence Proportion of individuals in a population with disease at a specific point of time Provides estimate of the probability or risk at one will be ill at a point in time Provides an idea of how severe a problem may be Useful for planning health services (facilities, staff)
  • 16. 16 # of existing cases of disease P = X 100 Total population at risk Formula for Prevalence
  • 17. 17 Cross-Sectional Study Example: Hypothesis: Obesity is a risk factor for knee osteoarthritis Sample: 100 women living in Iqbal town Lahore
  • 18. 18 Advantages Quick, easy, and cheap Can study multiple exposures and disease outcomes simultaneously Good for describing the magnitude and distribution of health problems
  • 19. 19 Disadvantages Mixes prevalent and incident cases Cannot determine the temporal association
  • 20. 20 ? Chicken or egg dilemma do not know whether the exposure preceded disease, or was a consequence of disease development. OR
  • 21. 21 Ecological Study An ecological study focuses on groups of people (rather than individuals) as the units of analysis Uses data from entire populations to compare disease frequencies between different groups during the same period of time or in the same population at different point in time
  • 22. 22 Cont The variables include measurements taken at the group level e.g. infant mortality rates of different countries A common type of ecological study design involves comparison of treatment patterns and outcomes of patients living in different geographical regions or countries; such studies attempt to make inferences about the quality of care provided by the respective healthcare systems.
  • 23. 23 Yearly mortality vs. antibiotics
  • 26. 26 Case-Control Study - Aims to identify factors that may contribute to an outcome. In this type of study, subjects are selected based on the outcome variable; subjects who have the condition (cases) are compared with the subjects who do not have the condition (controls). Looking back in the time, the cases and controls are compared with regard to exposure. (Noordzij, Dekker,Zoccali & Jager, 2009; 7 Lu, 2009)
  • 27. 27 Strengths Cheap, easy and quick studies - Multiple exposures can be examined - Rare diseases and diseases with long latency can be studied -Hypothesis generating
  • 28. 28 Limitations Case and control selection troublesome -Subject to bias (selection, recall, misclassification) -- Temporal relationship is not clear -- some potential to generate causal relationship
  • 29. 29 Proportions Exposed: Cases Exposed = a / a+c Controls Exposed = b / b+d
  • 30. 30 The Measure of Association in a Case- control Study Is the Odds Ratio d c b a D E D E OR = Odds of exposure among diseased Odds of exposure among non-diseased OR = a / c = a d b / d b c =
  • 31. 31 OR > 1.0 (Positive Association) The odds of exposure among cases is higher than the odds of exposure among controls. OR = 1.0 (No Association) The cases are equally likely to have the exposure than the controls. OR < 1 (Negative Association) the odds of exposure among cases is less than the odds of exposure among controls. Interpretation
  • 32. 32 Calculation of the OR in Case-control Studies Example: A Case-Control Study of Bladder Cancer Cases Control Smokers 112 176 Non-smokers 88 224 Total 200 400 thus, OR = ad/bc = (112 x 224) / (176 x 88) =1.6 Bladder cancer cases were likely to have smoked 1.6 times more than controls.
  • 34. 34 In a cohort study, an investigator defines a study population consisting of subjects who are free of the outcome of interest. This study design aims to determine which factors are associated with the development of this outcome. Depending upon the exposure status at the start of the study, subjects are classified as exposed or unexposed. Thereafter the subjects are followed over time to see who develops the outcome and who will not.
  • 35. 35 ineligible no participation deep chest SSI no deep chest SSI participation obese no participation deep chest SSI no deep chest SSI participation not obese CABG surgery performed at BJC hospitals during 1999 CABG patients Cohort Study
  • 36. 36 Relative Risk Measure of association between incidence of disease and factor being investigated Ratio of incidence rate for persons exposed to incidence rate for those not exposed Incidence rate among exposed RR = Incidence rate among unexposed Estimate of magnitude of association between exposure and disease
  • 37. 37 Incidence rate Incidence among exposed = a/a+b Incidence among non-exposed = c/c+d
  • 38. 38 Incidence rate among exposed RR = Incidence rate among unexposed Formula for relative risk: a / (a + b) RR = c / (c+ d)
  • 39. 39 RR > 1.0 (Positive Association) Risk is higher in exposed as compared to non exposed. RR = 1.0 (No Association) The risk is equal in the two groups. RR < 1 (Negative Association) The risk in the exposed is lesser than the non exposed. Interpretation
  • 40. 40 Cohort Studies Advantages & disadvantages: Can ascertain multiple outcome of single exposure High generalizability Hypothesis generating Can establish population-based incidence Accurate relative risk (risk ratio) estimation
  • 41. 41 Continue Temporal relationship can be inferred (prospective design) Magnitude of a risk factors effect can be quantified Multiple outcomes can be studied (smoking > lung cancer, COPD, larynx cancer) Time consuming and costly Loss to follow up ( participants can leave in between)
  • 43. 43
  • 44. 44 Experimental Study Defined A study in which the investigators determine and control the conditions of the experiment: Participants are randomly assigned to groups that experience carefully controlled interventions manipulated by the experimenter allowing causal inference about the effects of the interventions under investigation

Editor's Notes