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Question 1

define incidence, units?

Answer 1

An incidence rate is the number of new cases of the disease per 1000 people per year (or 1000 person–years)
E.g. 3 cases of colorectal carcinoma diagnosed per 1000 people per year

Question 2

define prevalence

Answer 2

Prevalence is the amount of people who currently have the disease in a set population (with no time frame)
E.g. 30 people per 1000 people have diagnosed colorectal carcinoma

p=(Ix length of disease)

Question 3

calculate the incidence rate ratio

Answer 3

If 300 new cases in a population of 30000 over a two year period were seen in an exposed region
And 400 new cases in a population of 60000 over a three year period were seen in an unexposed region
The incidence rate ratio will be
= (300 / (30000x2)) ÷ (400 / (60000 x 3)) = 2.25

(new case/ pop x no. of years) /(new case 2/ pop 2 x no. of years 2) =2.25

2.25 times as likely to die in place 1 than place 2

Question 4

describe relationship between incidence and prevalence

Answer 4

prevalence is stable if incidence rate = death/cure
if death/cure higher than incidence then prevalence decreases
incidence higher than death/cure then prevalence increases

Question 5

what are variations in risk

Answer 5

in population, not everyone has the same risk of disease e.g. overweight more likely to suffer MI

Question 6

why is systematic variation important

Answer 6

gives clues about cause of disease.

Question 7

why do you need a control group

Answer 7

control is the comparison group
compare levels of exposure in 2 groups to identify causal factor
may be able to then prevent exposure to reduce incidence

Question 8

incidence rate

Answer 8

new events/ person x years= events per person year

Question 9

incidence rate ratio

Answer 9

rate b (new/ exposed)/ rate a (old/ not exposed)
8 deaths in 800x1000= 10 in 1000 old
5 in 1000 new
rate b/ rate a= 5/1000 / 10/1000= 0.5
new treatments half the risk of death

Question 10

define rate

Answer 10

measure of absolute risk

Question 11

deifne ratio

Answer 11

measure of relative risk

Question 12

how can systematic variation be a nuisance

Answer 12

confounding factors (age/sex) cause spurious relationships if not taken into account

Question 13

how can you get rid of confounding factors

Answer 13

use age specific rate ratios: narrow age bands
standardised mortality ratio: shows rate ratio for 2 pop if age/sex structure were identical; age and sex arent confounding

Question 14

describe SMR

Answer 14

expected mortality in an age sex pop/ observed mortality in an age sex pop x100
100; same risk in study pop as control
>100 higher risk in study than control