4. Measures Of Occurence And Ch. 2 Of E-book

Question 1

What is incidence

Answer 1

The rate at which NEW cases occur in a population during a specified period
Must include time unit

Question 2

How is incidence rate calculated

Answer 2

Number of new cases in period/ number at risk in population in period

Question 3

When calculating incidence rate, why might the number of people at risk vary or lead to inaccuracies

Answer 3

People in a population can:

• be born or die
• recruited into/ leave study at different times
• actually get the disease so technically not in the group who are at risk of getting it

Question 4

What is prevalence/ point prevalence

Answer 4

How many people have a disease amongst a population at a specific time

Question 5

Equation of calculating point prevalence

Answer 5

Number of people with a disease at a certain time/ number of people in the population at that certain time

Question 6

Calculation for case fatality rate

Answer 6

Number of people who die from the disease in period/ number of people with disease in period

Question 7

Mortality rate of disease calculation

Answer 7

Number of people who die from the disease in period/ number of people in the population in period

Question 8

What is a stratum

Answer 8

A subgroup of your individuals in the sample

Question 9

What is adjustment

Answer 9

This is done when the crude rates that you have calculated may be refined to better represent the data.

Question 10

Prevalence calculation

Answer 10

Incidence rate x average duration of disease

Proportion of existing cases - old and new

Question 11

What is the prevalence pool

Answer 11

Cases living in the population with the disease
Excluding out-migration, death and cures (cases will decrease)
Add in migration (cases will increase)

Question 12

What is mortality

Answer 12

The incidence of death from a disease

Question 13

What are ‘person- weeks’

Answer 13

Adding all the number of weeks that each person is participating the study gives person- weeks.
Multiply by 52 to get person - years
For example, a study that followed 1000 people for 1 year would contain 1000 person years of data.

Question 14

Why ‘person years at risk’ are used

Answer 14

When following people over time, people in a population vary and this can lead to inaccuracies eg,
Be born or die
Recruited into or leave study
Actually get the disease and therefore are no longer risk of getting it

So person years looks at the actual total time that participants were exposed to the exposure