+Lecture 10 - Epidemiology and demography in health research / Epidemiological
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
3) Environment where the study takes place
-Popular / Lay epidemiology
Experimental versus Observational Studies
-exposure is varied to determine how many get the disease
-Occurrence of disease is observed in people who are exposed
-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
•Limitation – does exposure lead to outcome?
Types of Descriptive Studies
-Data from entire populations is used
-Cannot link exposure to disease in the same person
-Profile of a single person
-Describes the characteristics of a number of patients
Cross-Sectional Study Design
-Exposure and disease measured at one point in time
-Population of interest
-Temporal association cannot be clearly determined
-Individuals based on exposure status
-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
•Rate of those who develop the disease in the community?
When do we use Prospective Studies?
•Strong suggestion of association
•Exposure is rare
•Short average time between exposure and disease
• Time consuming
• Loss to follow-up
• Limited to rare exposures
• Ascertainment of disease
•Classification before the disease
•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
-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