Cohort Studies Flashcards
What makes up observational studies
Cohort studies
Case-control studies
Cross-sectional studies
What makes up interventional studies
- Randomised controlled studies
How does cohort studies work
- identify a large group of people (cohort)
- measure your exposure and see if they were exposed and unexposed
- follow them up over and time and see if the exposed or unexposed group get the disease or don’t get the disease and determine the disease occurrence
- relate the information on disease occurrence to exposure
Objective
To assess the impact of breast feeding on the risk of being overweight in children at the time of entry to school.
Methods
Mothers asked about breast feeding shortly after delivery and at 6 months.
At 5 years children were assessed physically.
is this a cohort study
Yes
- the disease is the child being overweight
- the exposure is breast feeding
Objective
To assess the impact of breast feeding on the risk of being overweight in children at the time of entry to school.
Methods
A group of overweight children were identified when they started school and the same number of normal weight children at the same school were identified.
Their mothers were asked about breastfeeding
Is this a cohort study
no
- it is a case control study
as the patients already have the disease and the researchers are working out what they are exposed to
What is the bias in cohort studies
Loss to follow-up
Exposure usually measured at just one time point
Selection of cohort
What are the disadvantages of cohort studies
Take a long time
Need a lot of people
Very expensive
If you were a non-smoker what was your risk of dying from lung cancer in 1 year ?
17 per 100,000 risk of dying from lung cancer in one year
What is incidence usually taken to be
INCIDENCE is usually taken to be a measure of RISK
What is incidence
Incidence = number of new cases (or deaths) of a disease per 100,000 people per year
What is the relative risk
Relative risk = incidence of disease in exposed population/ incidence of disease in unexposed population
How do you investigate if something has arisen due to chance alone
P values
Confidence Intervals
what is the difference in confdience internals for means and relative risks
- If the 95% CL for a difference in means includes 0 then the result is not statistically significant
- If the 95% CI for a difference in means excludes 0 then the result is statistically significant
- If the 95% CI for a relative risk includes 1 the result is not statistically significant
- If the 955 CI for relative risk excludes 1 then the result is statistically significant
What is a cofounder
A confounder is a factor that is associated both with the exposure and also with the disease.
What curve can be used for survival analysis
Kaplan-Meier curves
