1.2 Basic Measurements

Question 1

Define Prevalence

Answer 1

The proportion of individuals in a population who have a disease or an attribute at a specified point in time.

Prevalence = No. with disease at a point in time/total no. in population

Can be reported as a proportion, percentage or per 100^n people.

Question 2

Define: Incidence

Answer 2

The number of new health related events in a defined population within a specified period of time.

Question 3

Cumulative Incidence (CI)

Answer 3

Measures the proportion of people with disease at start of specified time period

CI = Number who develop disease in specified time period / Number at risk of getting disease at start of time period

Expressed as proportion or percentage

Question 4

Incidence Rate (IR)

Answer 4

Measure how quickly people are developing the disease

IR = Number who develop disease / number person-time when people were at risk of getting disease

Expressed as a function of time (i.e person years)

Question 5

Person-Time

Answer 5

The product of the amount of time multiplied by the number of members of a population who have been affected by a certain condition.

Each person contributes one person-year to the denominator for each year (or day, week, month) of observation before disease develops or is lost to follow-up.

Question 6

How are prevalence and incidence related?

Answer 6

Depends on how long disease persists before cure or death.
Prevalence = Incidence rate x average duration of disease
Assumes a stationary population and prevalence of disease is rare

Question 7

What increases prevalence?

Answer 7

o	Long duration of disease
o	Incidence rate increase
o	In-migration of cases
o	In-migration of susceptible/at risk
o	Out migration of healthy people
o	Improved diagnostics / better reporting

Question 8

What decreases prevalence?

Answer 8

o	Shorter duration
o	High case-fatality
o	Decrease in incidence
o	In-migration of healthy people
o	Out-migration of cases
o	Improved cure rate

Question 9

How to calculate Mortality Rate?

Answer 9

Number of deaths in a given period / population at risk of death over that period

Question 10

How to calculate survival rate?

Answer 10

Number of patients still alive from diagnosis to given period / total number of patients over that period.

Question 11

What are some of the ‘Total Health Measures’?

Answer 11

Burden of Disease
Life Expectancy
Disability-Free Life Expectancy
Quality Adjusted Life Years 
Health Adjusted Life Expectancy