Lecture 10

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4 Apr 2011
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+Lecture 10 - Epidemiology and demography in health research / Epidemiological
research designs
Epidemiology: "the study of the distribution and determinants of health-related states in
specified populations, and the application of this study to control health problems."
Demography: The scientific study of human populations, including their size,
composition, distribution, density, and growth as well as the causes and socioeconomic
consequences of changes in these factors. (World Bank)
Types of Epidemiology
1)Level upon which research focuses
-Internally, within the body - Clinical epidemiology
-Behaviorally - Social epidemiology
-Contextually / structurally - Critical epidemiology
2) Type of disease
-Communicable-disease epidemiology
-Chronic-disease epidemiology
3) Environment where the study takes place
-Community epidemiology
-Occupational epidemiology
4) Tools
-Quantitative epidemiology
-Popular / Lay epidemiology
Experimental versus Observational Studies
Experimental:
-exposure is varied to determine how many get the disease
-Unethical
Observational:
-Occurrence of disease is observed in people who are exposed
Study Designs
Descriptive Studies
-Disease and related factors are measured
-e.g. incidence data, prevalence data, mortality data.
When do we use descriptive study designs?
-Health problem is suspected
-Hypotheses formulation
Limitation does exposure lead to outcome?
Types of Descriptive Studies
Correlational studies
-Data from entire populations is used
-Cannot link exposure to disease in the same person
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Case reports
-Profile of a single person
Case series
-Describes the characteristics of a number of patients
Cross-Sectional Study Design
-Exposure and disease measured at one point in time
-Survey
-Population of interest
-Temporal association cannot be clearly determined
Analytical Designs
Prospective Cohort
-Individuals based on exposure status
-Follow-up period
-Are exposed more likely to develop disease?
e.g. Does spending time in a hospital with a known case of SARS increase the risk of
encountering the disease?
Rate of disease in people who develop SARS after being admitted to
the hospital?
Rate of those who develop the disease in the community?
Compare
When do we use Prospective Studies?
Strong suggestion of association
Exposure is rare
Short average time between exposure and disease
DisadvantagesAdvantages
Expensive
Time consuming
Loss to follow-up
Limited to rare exposures
Ascertainment of disease
Classification before the disease
develops
calculation of incidence rates among
exposed and not exposed
calculate risk directly
observation of many outcomes
Efficient for rare exposures
Historical Cohort Retrospective Design
-Cases based on exposure status
-Retrospective examination
-Medical records, interviews, or surveys
-Time of disease development cannot be ascertained
-Study design requires less time
Case Control Study Designs
Selected on basis of disease
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