Cohort Studies Flashcards
Cohort Studies
Compares risk in one group of people (cohort) with another group
Follows disease-free individuals and moves forward in time
How is a cohort study better than a case control study
Cohort is proactive so avoids recall bias and allows for better measurement
People might not know whether habits changed after risk comes true
Describe the design of a cohort study
Advantages of Cohort studies
Measurement of incidence
Can be more sure about temporal effects of exposure
Easier ethically
Avoid recall and selection biases
Disadvantages of cohort studies
Time intensive/expensive
Inefficient for rare diseases
Confounding
Drop-outs
Healthy worker effect
Attrition Bias
When dropout frequency is related to exposure to certain outcome, skewing the results (e.g. drug users being more likely to be lost to follow up than non drug users)
Retrospective Cohort Study
What it sounds like
Using past collected data
Healthy worker effect
Workers are healthier than general population so this is a disadvantage of retrospective cohort studies when they data is based on workers
Incidence Rate
Number of new cases arising in a given period in a specified population
(Number of new cases of disease)/(total person time at risk)
Interpret a rate ratio of 0.13 when comparing risk of colorectal cancer development in those with high vs low fruit/vegetable consumption
Rate of colorectal cancer among those with high consumption of f/v is 87% lower than the rate among those with low
How to calculate rate ratio
Rate of disease in exposed group/rate of disease in unexposed group
Survival Analysis
Allows description and comparison of:
Number of people who suffer an event of interest
Time at which event occurs
(e.g. risk of death after surgery or recurrence of cancer post treatment)
Median Survival
The age at which 50% of subjects are still alive
