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Research Synthesis (meta-analysis)

Case Study

Single subject Design

Epidemiology (Case control and Cohort)


Historical (Archival)

Epidemiology Research

What is Epidemiology?
 “the  study  of  the  distribution and determinants of health related states or events in specified populations, and the application of this study to the  control  of  health  problems”  (Last,  1988)

Epidemiology Research Terminology
 Distribution—relates to the frequency and
patterns of disease occurrence in a population  Frequency  Prevalence or how often the disease occurs. (e.g., ., in 1996 the prevalence of all cardiovascular diseases in the US was estimated to be 58,800,000 people/or 25% of the population—American Heart Association, 1998)  Incidence/occurrence—rate of new disease or health events (e.g., the mortality rates for cardiovascular disease were 304 per 100,000 in the US in 2001(Centre for Disease Control and Prevention, 2004)

Epidemiology Research Terminology
 Distribution—relates to the frequency and patterns of
disease occurrence in a population

 Pattern  Refers to characteristics related to:  person (e.g., age, gender, ses)  place (e.g., urban-rural)  time (e.g., annual, seasonal, daily patterns) that are often useful in developing hypothesis about risk factors for the disease.

Why is Epidemiological Research Important?
 It is virtually the only way in which a
quantitative understanding of the exposuredisease/health risk relationship can be obtained.

 E.g., It would be unethical to randomize a
group of individuals to either a drinking or nondrinking condition, wait 10 years and then see how much death and disease, drinking causes.

Epidemiological Research
 Epidemiological research is observational not
 E.g., A portion of the population chooses to drink while others do not. Epidemiologists use these naturally occurring  differences  in  a  population  to  “observe”  and   therefore understand the effect of these differences on specific disease outcomes.

Epidemiology Research
 Are used to provide the scientific backbone for
public health endeavors, including:
 i) quantifying the magnitude of health problems  ii) identifying factors that cause disease (i.e., risk factors)  iii) providing quantitative guidance for the allocation of public resources  iv) monitoring the effectiveness of prevention strategies using population wide surveillance programs (Caspersen, 1989)

Types of Epidemiologic Study Designs
Crosssectional Ecological

Casecontrol Cohort

 “general  observations  concerning  the  
relationship of diseases to basic characteristics such  as  age,  sex,  race,  occupation”  (Last,   1988).

 Cross-sectional  Ecological

Descriptive: cross-sectional
 E.g., examining the relationship between physical activity and health outcomes, such as cardiovascular disease.

Active Inactive

Measure cardiovascular risk factors

 Examine the mean differences.  Limitation: Outcome variables are typically measured a single time point.

Descriptive: ecological
 Ecological studies use existing data sources
(e.g., census data) for both exposure and disease outcomes to compare and contrast rates of disease by specific characteristics of an entire population.

Morris et al (1953, Lancet)
 Included in their seminal work was an ecologic study of
heart disease mortality and occupational physical activity

 Investigators tabulated heart disease mortality rates by age and occupational activity level among Englishmen and Welshmen using existing public health statistics for the years 1930 and 1932

Morris et al (1953, Lancet)
Mortality (per 1,000,000)
*The data here show a graded inverse relationship.

Descriptive: ecological
Research Example - Morris et al. (1953)

 Reported a series of

studies that used occupational classifications as a...
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