Cohort study Flashcards
What is a cohort study?
Identifies a group of people and follows them over a period of time to determine incidence of specific disease(s) and see how measured exposures affect their outcome
Where are cohort studies in the hierarchy of evidence?
Third from the top
What are three ways that disease can be measured?
- Prevalence
- Risk
- Incidence Rate
What is the equation for prevalence?
= number of individuals with disease at a particular time / total number in population at risk at that time
What is the definition of prevalence?
The proportion of people that have disease at a particular point in time.
What is the equation for risk?
= number of new cases of disease in a time period / number of people in population, disease free at outset
What is incidence rate and what is the equation for it?
Incidence rate = how fast the number of new cases of disease is occurring
= number of new cases in a time period /
total number in population disease free at outset x time interval
Can prevalence and incidence be related?
Prevalence and incidence can sometimes be related:
Prevalence of disease can increase due to
- incidence increasing
- the average duration of people living with
the disease has increased - increasing pool of
prevalent cases
What is the equation for RISK?
RISK = Number of new cases of disease (d) / Number initially disease free (n)
What is the equation for risk ratio (RR) ?
RR = RISK of outcome occurrence in exposed (d1/n1) / RISK of outcome occurrence in unexposed (d0/n0)
What does a RR > 1 mean?
It suggests that exposed group have increased risk of outcome (disease).
The risk in the exposed group is greater than the unexposed.
What does a RR < 1 mean?
It suggests that the exposed group have a decreased risk of outcome
Which group out of the exposed or unexposed group is the baseline comparator (the reference group)
Usually the unexposed group
How do you work out the risk difference?
= Risk in exposed - Risk in unexposed
(have units e.g. risk per 100)
What are the strengths of a cohort study?
+ Exposure is measured before the onset of
disease
+ Demonstrate direction of causality
+ Multiple outcomes (diseases) can be studied
for any one exposure
+ Can look at multiple exposures
+ Rare exposures can be examined by
appropriate selection of study cohorts
+ Can measure incidence and prevalence
