Frequencies Contd

Question 1

What is incidence?

Answer 1

New cases of the disease

Question 2

What is prevalence?

Answer 2

Existing cases of the disease + new cases of the disease.

Question 3

How do you calculate incidence?

Answer 3

of new cases/ # of people at risk for the disease

• If you know the source of the disease, only people around the source would be in the denominator.
• time frames for numerator and denominator must be the same
• not very precise in dynamic populations
• usually getting a pop count is an estimate
• remember to leave out the people who already have it and the ppl who are immune

Question 4

What is person-time

Answer 4

A way to equal the size of source population and length of time.

Ex: 100 person- years means 2 people for 50 years or 100 people for 1 year or 10 people for 10 years etc..

Question 5

What is incidence density?

Answer 5

of new cases/ total person-time of population at risk

This is used for dynamic populations
* everybody is being followed at different times

Question 6

What are the three key factors in comparing frequencies in groups?

Answer 6

1. Number of people impacted
2. Size of the source population
3. Length of time the source population is followed
   * size and length of time must be the same.