Lecture 4 8/28/24

Question 1

What is a disease count?

Answer 1

-total number of conditions in a population
-expressed as a whole number
-dimensionless/no unit
-values range from 0 to infinity

Question 2

What is a disease proportion?

Answer 2

-fraction with numerator included in the denominator
-often expressed as a percentage
-dimensionless
-values range from 0 to 1 (0 to 100%)

Question 3

What is a disease rate?

Answer 3

-fraction with numerator included in the denominator, but with a direction
-not dimensionless/per unit of something
-no upper bound

Question 4

What is a ratio?

Answer 4

-fraction where numerator is not included in the denominator
-dimensionless

Question 5

What are the measures of morbidity?

Answer 5

-attack rate
-incidence count/incident rate
-prevalence

Question 6

What are the measures of mortality?

Answer 6

-mortality rate
-case fatality rate

Question 7

What is morbidity?

Answer 7

cases/total population

Question 8

What is an attack rate?

Answer 8

number of animals developing disease during specific time period following exposure/total number of animals exposed

Question 9

What is mortality?

Answer 9

deaths/total population-time at risk

Question 10

What is case fatality rate?

Answer 10

total # death from disease X during time period/total # animals acquiring disease X

Question 11

What is incidence?

Answer 11

the number of new cases of disease within a given time period

Question 12

What is prevalence?

Answer 12

the number of existing cases at a point in time/time period

Question 13

Why is it important to distinguish incidence and prevalence?

Answer 13

-magnitude may vary drastically
-factors associated with acquiring new disease may be different from those associated with disease
-temporal issues for causal inference

Question 14

What are the factors that influence patterns of disease occurrence?

Answer 14

-true increases or decreases in disease occurrence
-changes in sensitivity and/or specificity of surveillance system
-mistakes made in collecting and/or organizing data
-changes in the perceptions of the public or the health care community about importance of disease diagnosing/reporting

Question 15

What are the factors that influence long-term increases in incidence?

Answer 15

-introduction of a new disease agent into a population
-decreasing effectiveness of control measures
-changes in environment
-changes in societal practices

Question 16

What is the calculation for incidence?

Answer 16

new cases/population-time at risk

Question 17

What is the calculation for prevalence?

Answer 17

old and new cases/population at risk

Question 18

How does point prevalence differ from period prevalence?

Answer 18

-point prevalence is measured at one specific time
-period prevalence is measured over a range of time

Question 19

How is period prevalence measured?

Answer 19

(# of cases at beginning of time period + # of cases that develop during period)/size of pop. during time period