7: Evidence based medicine 2

Question 1

What is a cohort study?

Answer 1

Comparisons of groups of a population who were a) exposed b) not exposed to a certain thing

e.g those exposed to radiation after Hiroshima/Nagasaki atomic bombings

Question 2

In a cohort study, you start with a population with different incidences of a thing and work (forwards / backwards) to figure out what caused this difference.

Answer 2

backwards

Question 3

In a cohort study, you can either

a) start with a population and follow them going forwards
b) go back and examine differences in a population

What are these types of study called?

Answer 3

Prospective cohort study

Retrospective cohort study

Question 4

A cohort study allows you to estimate the ___ of something occuring in a population.

Answer 4

risk

Question 5

In a cohort study, the population you have needs to be a ___ population.

Answer 5

general

otherwise you don’t know what’s typical/rare

Question 6

What size of population do you need to pick up rare diseases in a cohort study?

Answer 6

Large sample size

Question 7

What is relative risk?

Answer 7

Relative risk = Probability of event (incidence) when exposed / Probability of event (incidence) when not exposed

Question 8

What is relative risk also known as?

Answer 8

Risk ratio

Question 9

When there is no difference between two populations, the relative risk is _.

Answer 9

1

Question 10

If the risk ratio is < 1, the exposed population are (protected from / vulnerable to) the effect.

Answer 10

protected from

Question 11

If the risk ratio is > 1, the exposed population is (protected from / vulnerable to) the effect.

Answer 11

vulnerable to

Question 12

What is absolute risk?

Answer 12

Absolute risk = Risk in exposed group - Risk in non-exposed group

Question 13

What is a case control study?

Answer 13

Find two populations, one with the condition and one not

Take identical histories and compare them

Draw conclusions

Question 14

Cohort studies tend to go ___ in time while case-control studies go ___.

Answer 14

forwards

backwards

Question 15

Case control studies are good for studying ___ diseases.

Answer 15

rare

Question 16

What statistic is associated with case control studies?

Answer 16

Odds ratio

Question 17

How is an odds ratio calculated?

Answer 17

Odds ratio = Odds of event when exposed / Odds of event when not exposed

Question 18

An odds ratio of < 1 means that the risk is (lower / higher) in the exposed group.

Answer 18

lower

Question 19

An odds ratio of > 1 means that the risk in the exposed group is (lower / higher) than the risk in the non-exposed group.

Answer 19

higher

Question 20

Can causation be proved by a case-control study?

Answer 20

No

histories rely on memory