Lecture 5A, part 2 Flashcards
What is assessed at the same time in cross-sectional studies?
Exposure and outcome
What studies can infer causality?
Experimental
In experimental studies, who assigns and exposure and non-exposure?
Investigator
Strengths of ecological studies
Quick, easy, and inexpensive
Useful for looking at the impacts of large-scale changes or interventions
Ecologic effects may be of interest/transmission dynamics at the pop level
Limitations of ecological studies
May be difficult to detect subtle or complicated relationships
Cannot look at cause and effect in individuals
Ecological fallacy/bias
Definition of ecological fallacy/bias
An error in deduction that involves deriving conclusions about individuals solely on the basis of group data analysis
-An association btwn variables on an aggregate level does not necessarily represent the association that exists at the individual level
Components of experimental studies
Research question involves a prevention or tx
Small effect expected
Trial is ethical, feasible, and financially possible
Components of observational studies
Research question involves a prevention, tx, or causal factor
Moderate or large effect expected
Trial not ethical, not feasible, or too expensive
Experimental study definition
Any study in which the investigator actively manipulates the exposure to evaluate the role of that exposure in the prevention or tx of dz
What are common types of experimental studies?
Field trials
Community trials
Clinical trials (early phases)
Randomized control trials (considered the “gold standard” of epidemiological research)
Pragmatic trials
Strengths of experimental studies
Reduces variation by extraneous factors through 3 strategies: randomization, placebo, blinding
Good info on exposure and dz
Study pop chosen based on eligibility criteria, clearly defined comparison group
Limitations of experimental studies
Study pop must be large enough to detect whether there is a true difference between the tx and comparison groups
Ethical issues (cannot study harmful effects)
Non-compliance, f/u
Very expensive, time-consuming
Non-experimental studies include ______ and ____ studies
Cohort, case-control
What is the goal of non-experimental (observational) studies?
Simulate the results of an experiment had one been possible
What is involved in cohort studies?
Follow a group of ppl with a common characteristic or experience (the cohort) over time and measure the occurrence of dz across predetermined exposure or risk categories
Selection process in cohort studies
Select ppl without the outcome of interest, categorize them based on their exposure, and follow for the development of dz
How are ppl classified in cohort studies?
Based on their initial exposure date
How can special cohorts be used in cohort studies?
To study the health defects of rare exposures
Timing of cohort studies
Can be either prospective or retrospective
Strengths of cohort studies
Clearer temporality
Efficient for investigating rare exposures
Can evaluate a large number of possible health effects of a single exposure
Limitations of cohort studies
Data collection- need reliable sources of data for exposures, outcomes, and confounders over time
Time and money
Loss to f/u, not good for dynamic pops
What is involved in case-control studies?
Select ppl with the outcome of interest (cases) and ppl without the outcome of interest (controls) and then classify them all according to their exposure status
Who are ppl selected in case-control studies?
Based on their outcome status
In comparison to cohort studies, how are case-control studies viewed?
Inferior alternative
What is the modern view of case-control studies?
They are an efficient way to learn about the relationship between an exposure and a dz
