Cohort studies - quiz Flashcards
What are the two things that cause and effect under cohort studies are necessary ?
1) Temporality
2) two time points
what are the pros of a cohort study?
1) Provides direct estimate of risk
2) useful for rare exposures
3) can study more than one outcome
4) temporal relationships are more clear
what is the formula for number of non- exposed subjects?
C+D
What are the two things that cohort studies are based on ?
1) they are population based
2) they are exposure based
what is the difference between a cohort study in a retrospective point vs a case-control study in a retrospective point?
Cohort study uses entire cohort study of exposed people , while case control uses cases and controls who do not represent entire cohort of exposed.
what is a cohort study ?
a study of population group or subset that is followed over a period of time
what are the disadvantages of a cohort study?
1) Larger, longer, more expenses
2) prone to bias like attrition, and misclassification
3) not useful for rare diseases.
what is the healthy worker effect bias mean ?
people with severe illnesses excluded from employment, but not from the general population. As a result, comparisons of mortality rates btw an employed group and the general population will be biased.
What is the most important characteristic of cohort studies?
Almost always a primary data collection, and is always identified based on exposure status.
what is a population based cohort study mean ?
entire population or representative sample
what is the incidence of disease in non-exposed group?
C/(C+D)
what happens in a prospective study?
two groups, exposed and non exposed are followed up over time to see who has the outcome and who does not.
What are some things to keep in consideration for cohort?
1) availability of exposure data
2) size and cost
3) data collection and data management
4) follow-up issues
5) follow-up issues
6) sufficiency of scientific justification
what does exposure based cohort study mean ?
based on exposure of interest, and comparison groups
What kinds of bias can occur in a cohort study?
Selection bias, confounding, and even misclassification
what are some cohort study characteristics ?
1) use individual data
2) Identified Based On Exposure Status
3) Can be retrospective or prospective
4) Able to evaluate multiple outcomes
5) give information on incidence
6) almost always a primary data collection
what is the formula for Relative risk in words?
incidence rate in exposed / incidence rate in non-exposed
what is the measure of association for cohort studies?
relative risk (RR)
what is the name of cohort studies used? Define them:
Prospective/ longitudinal study
Definiton ^ : starts with group of people without outcome that we are interested in studying, but they are at risk of it.
What do cohort studies try to understand ?
the cause and the effect
what happens in the retrospective cohort study?
How do we measure it ?
this is the one where we use historical data to find the exposure level at baseline in the past.
We follow-up for Disease between baseline and the present.
what is the incidence of disease in exposed group?
A/ (A+B)
What is the relative risk formula in terms of a 2x2 contingency table?
[ a/(a+b) ] / [ c/(c+d) ]
what is the formula for number of exposed subjects ?
A+B
what is the cohort effect?
the influence of a membership in a particular group: this changes exposure/ outcomes due to membership on group
NOTE: membership means same as relationship in group. Friendship in group. etc.
What are some other measure of association to consider for a cohort study?
Rate ratio
Attributable risk
Population-Attributable Risk
What does the term attrition under selection bias in a cohort study mean ?
Loss-to-follow up, especially problematic of differential
