Cohort Studies

Question 1

What is a cross sectional study?

Answer 1

One where the exposure and disease status of patients is measured st a single point in time only

Question 2

What is the prevalence ratio?

How is this calculated?

Answer 2

The prevalence of the disease in the exposed

Divided by

The prevalence of the disease in the non-exposed

See notes for help.

Question 3

What is the prevalence odds ratio?

How is this calculated?

Answer 3

The odds that a diseased person was exposed to the exposure in question

It is the cross table multiply and divide (see sheet for help).

Question 4

What are the prevalence odds?

How are these calculated?

Answer 4

The odds that a diseased person was exposed

And

The odds that a non-diseased person was exposed

Question 5

With respect to cohort studies, what X3 time frames can they cover?

Answer 5

1) retrospective
2) prospective
3) bi-directional

Question 6

What is the relative risk (incidence proportion or cumulative incidence)?

Answer 6

It is the number of new cases out of the people at risk at the start of the study (times stated number)

It looks at the stats at the end of a given period of time, whereas relative risk (ID) looks at the rate of development of a disease.

Question 7

What is the relative rate (incidence rate or density)?

Answer 7

It is how fast a disease develops

It is the number of new cases / total person-time years

Question 9

What is the rate ratio in cohort studies?

Answer 9

The rate of disease in the exposed

Divided by

The rate of disease in the unexposed

= a/(a+b) / c/(c+d)

Question 10

What are person years?

Answer 10

It is a way of defining the number of cases observed in a time frame when different participants contribute different lengths of time to the study.