1- epidemiological concepts

Question 1

Define prevalence

Answer 1

Proportion of pop who have a disease at a relevant time
= existing cases/total pop
- done at single point in time/over a period

Question 2

Define period prevalence

Answer 2

Proportion of pop affected over a given time

Question 3

Incidence

Answer 3

No of new cases of disease in a given pop over a given period of time
= N new cases over time period/total pop at risk
- calc over a standard time unit (ie a year) or longer periods

Question 4

Diseased Healthy

Exposed A B

Not exposed C D

Answer 4

Risk- prob an event will occur
risk in exposed A/A+B
Not exposed C/C+D
out of all A+C/A+B+C+D

Question 5

Define rate

Answer 5

No of events occurring in a pop at a given time

Measure of frequency

Question 6

Calculate odds

Answer 6

A/B

Question 7

Calculate relative risk

Answer 7

Risk in exposed/ risk in unexposed

Question 8

Rare diseases- RR?

Answer 8

Numerically similar ratios

Question 9

Calculate risk difference

Answer 9

Subtract one risk from another

Question 10

Define attributable risk

Answer 10

Difference in risk of condition between exposed and unexposed populations, assuming the exposure is causally related to the disease

Question 11

Define and calculate numbers needed to treat

Answer 11

Average no of pts who need to be treated to prevent 1 additional bad outcome
= 1/reduction in absolute risk

Question 12

Number needed to harm

Answer 12

equivalent statistic for harmful outcomes