Epidemiology 9-cohort studies Flashcards
What is a cohor study ? what does it compare ?
A group of exposed individuals and a group of nonexposed individuals and follows up both groups to compare the incidence of disease in the two groups.
In a cohor study if there a positive association that exist between individuals and a group of nonexposed individuals then ? Which group would have the higher proportion ?
Cohort study If a positive association exists between the exposure and the disease •we would expect that the proportion of the exposed group in whom the disease develops would be greater than the proportion of the nonexposed group in whom the disease develops. Cohort studies Gordis,
Draw a diagram on how a cohor study works ? between ex[psed and not exposed group
Draw another diagram of cohor study between smokers and non smokers .
What is temporal association ? What must happen to prove there is a temporal association ?
Two or more events that occur around the same time but may be unrelated, chance occurrences.
Cohort studies
New cases of disease will occur
•To determine a temporal association between exposure and disease
–Exposure preceded the disease
What are three things that cohor study and clinicl trails share ?
Cohort studies & clinical trials
- Both designs compare exposed with nonexposed groups
- Ethical reasons we cannot randomize persons to receive a harmful substance
- Smoking
- Presence vs. absence of randomization
What is Occupationally cohorts and what is community to a cohor study ?
Cohort studies
•Study population by selecting groups for inclusion in the study on the basis of the exposure
–Occupationally cohorts
•To select a defined population before any of its members become exposed or before their exposures are identified
–Community
What must happen in a cohor study to get an outcome ?
Cohort studies
•An outcome to develop in a population
–Long follow-up period lasting until enough events have occurred
Draw a diagram of a population that has been randomly selected vs not
What is a prospective study ?
What is a retrospectve study ?.
looking back on or dealing with past events or situations
.What is prospective cohor study ? What are two examples of it? what does it mean ?
What are ways retrospective cohort study can gain their information ?
Cohort studies
•Retrospective cohort study
–Historical cohort study
–No concurrent study
- We are still comparing exposed and non exposed groups
- We will use historical data from the past
In a retrospective cohort study , when is exposure measured ? and when is the outcome ?
Exposure is ascertained from past records
•Outcome (development or no development of disease) is ascertained at the time the study is begun
What are some retrospective Bias ?
Cohort studies
- Bias in assessment of the outcome
- Information bias:Information bias refers to bias arising from measurement error.
•Biases
–Nonresponse :Sometimes, in survey sampling, individuals chosen for the sample are unwilling or unable to participate in the survey. Nonresponse bias is thebias that results when respondents differ in meaningful ways from nonrespondents. Nonresponse is often problem with mail surveys, where the response rate can be very low.
–Losses to follow-up:In the clinical research trial industry, lost to follow-up refers to patients who at one point in time were actively participating in a clinical research trial, but have become lost (either by error in a computer tracking system or by being unreachable) at the point of follow-up in the trial.
