WEEK 7: COHORT, CASE CONTROL STUDIES Flashcards
what are cohort studies
Involve the formation of a cohort, which is a group of individuals followed over time
points to a cohort study
- More expensive, time consuming
- Not efficient for diseases with long latent periods
- Better exposure and cofounder data
- Less vulnerable to information bias
retrospective cohort study
A retrospective cohort study looks back in time. It uses preexisting secondary research data to examine the relationship between an exposure and an outcome. Data is collected after the outcome you’re studying has already occurred
- cheaper, faster
- more vulnerable to bias
prospective cohort study
a prospective cohort study follows a group of individuals over time.
- starts at the cohort
Incidence (Rate) Ratio - Relative Risk in Cohort Studies
Comparison of the incidence of a characteristic in 2 independent populations (or independent subpopulations) calculated by taking a ratio of their incidence rates
- exposed vs. unexposed
advantages of cohort studies
- Valuable when exposure is rare
- Can examine multiple effects of a single exposure
- Easier to determine the temporal relationship b/w exposure and outcome
- Allows measurement of incidence
incidence
the # of new cases of disease in a population during a specified period of time
Reported in terms of incide rate or an incidence population
formula of odds ratio
(odds of disease in exposed/odds of disease in unexposed)
2 necessary requirements for selection of controls
- controls must come from the same source population as cases
- controls must be selected independently of exposure
population based control
control selected from the general population, most suitable when cases are from well-defined geographic areas
nested controls
controls selected from an existing cohort population. Controls represent a subset of the full source population
hospital/clinic based controls
controls selected from among patients at a hospital or clinic
case control studies advantages
- More efficient than a cohort study (in terms of time, money, and effort)
- Suited to diseases with long latent period
- Optimal for rare disease
- Can examine multiple exposures
disadvantages of case control studies
- Exposure is assess after development of the outcome
May be unsure about temporal sequence b/w exposure and disease
Recall bias - Prone to selection bias in control choice - especially if response rates are low
- Can only study 1 disease or outcome
- Inefficient for rare exposures
- Can NOT calculate aboke measure of association
individual vs frequency matching
Individual matching - performed participant by participant
Frequency matching - providing similar distributions of confounders in groups
what is censoring
occurs when participants in a prospective vs longitudinal study die, drop out, are lost to follow-up, or are removed from further analysis
Population Attributable Risk Percentage (PAR%)
the proportion of incident cases in the total population that can be attributed to some people having the exposure
what is the rate difference
absolute difference in the incidence rate b/w the exposed group and the unexposed group (also called excess Rise, Attributable Risk, + isk difference)
Ex. if 10% of the unexposed and 15% of the exposed became ill during the study period, the excess risk in the exposed was 15%-10% = 5%
what is a proportion
- a ratio in which the numerator is a subset of the denominator (such as the denominator consisting of all study participants and the numerator including only females over 60 yrs of age)
what is loss to follow up
the inability to continue tracking a participant in a prospective or longitudinal study bc the person drops out, relocates, or dies or stops responding
what is a case control study
study that compares the exposure histories of people with disease (cases) and people w/out disease (controls)
what is a case
study participant with the infectious or parasitic disease, non-communicable diseases, neuropsychiatric conditions, injury, or other disease, disorder, disability, or health condition of interest to the researcher
what are the 3 options for matching
- No matching
- Frequency (group) matching
- Matched pairs (individual) matching
measures of association
refers to a # that summarizes the relationship b/w an exposure and a disease outcome
what is the measure of association for case control studies
odds ratio
what is a fixed population
all participants start the study at the same time and no additional participants are added after the studies start date
incidence rate
the # of new cases of disease in a population during a specified period of time divided by the total number of people in the population who were at risk during that period
- sometimes called the absolute risk
Cumulative Incidence/Incidence Proportion
the % of people at risk in a population who develop new disease during a specific period of time
