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Lecture 1

11:709:493 Lecture Notes - Lecture 1: Randomized Controlled Trial, Observational Study, Ecological Study

Nutritional Sciences
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Epidemiologic Study Design
Study Designs
- Can be classified as observational or experimental
o Differences:
In observational studies, the investigator DOES NOT
assign interventions/exposures, but rather observes
subjects and measures of variables of interest
inferences are limited to descriptions and
associations, NOT causation
In experimental studies, the investigator ACTIVELY
ASSIGNS individuals/groups to
interventions/exposures under study
It is possible to make inferences about
- Examples
o Observational:
Cohort (prospective or retrospective)
o Experimental:
Randomized controlled (clinical) trial
Non-randomized trials
o Natural experiments
- Hierarchy of Scientific Evidence (higher up = better evidence)

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o Meta-analysis of RCTs
o Systematic review
o Randomized control trial
o Non-randomized studies
o Cohort studies
o Case control studies
o Cross sectional studies
o Ecological studies
- Why design is best?
o depends on the study question
what is the current knowledge on the topic?
How common is the disease/risk factors?
How long would the study take?
What is the budget?
Are their ethical issues involved?
Cross Sectional Studies
- Observational study conducted at a defined point in time with
one measurement per unit of analysis
- Allows you to estimate the prevalence of a disease
o Group 1, group 2, group 3 = compared at one time
- Advantages:
o Cost-efficient
o Short duration
o Easy to implement
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