Measuring disease

Question 1

define prevalence

Answer 1

the number of cases at one point in time

e.g. 80 patietns in a population of 1,500
point prevalence =80/1,500 = 53 per 1,000 = 5.3%

is a proportion NOT a rate
denominator is persons not person per time
study is a cross sectional survey no follow up

Question 2

relationship between incidence and prevalence equation

Answer 2

prevalence = incidence x length of disease

Question 3

relationship between incidence and prevalence

Answer 3

incidence feeds into prevalence and death and cure feed out of prevalence

Question 4

what is the importance of systematic variation in risk of disease between groups?

Answer 4

as a useful source of information about causes of disease

as a nuisance which needs to be controlled for

Question 5

define incidence rate ratio

Answer 5

the rate of B exposed / rate of A unexposed

can be used to compare the effects of two treatments
e.g. number of deaths with new drug/ number of deaths with old drug

Question 6

define incidence and incidence rate

Answer 6

the number of instances of illness commencing, or of person becoming ill during a given period in a specified population
incidence rate = new evetns / person x time (years) = events per persons per year

allows comparisons to be made

Question 7

define absolute risk

Answer 7

measures the size of a risk in a person or group of people.
could be risk of developing a disease in a time period, or measure of the effect of treatment

it is a RATE

Question 8

define relative risk

Answer 8

it is a ratio
compares a risk in two different groups of people and wheather a particular group increases or decreases the risk of developing certain diseases

Question 9

define confounding factor

Answer 9

a confounder can distort the true relationship between two characteristics.

Question 10

Define standard mortality ratio

Answer 10

is a summary figue comparing the level of mortality observed in a study population with the level of mortality expected if a standard reference populations age-sex specific rates were applied to the study population age-sex groups.
SMR accounts for any age-sex confounding
usually expressed as a percentage

Question 11

systematic variations in incidence rate ratio is useful…

Answer 11

in searching for causes of disease
treatment effects

can also be a nuisance