How do we measure disease

Question 1

What are some factors to consider when measuring disease?

Answer 1

• who was attacked ?
• when did the disease occur?
• where did the case arise?

Question 2

What is incidence?

Answer 2

number of new events in the population over the certain time

Question 3

What does measuring incidence require?

Answer 3

• requires two or more measurements to individuals were disease free at the start
• measures the number of disease events → measure of risk (accounts for duration of disease)

Question 4

What is incidence a measure of?

Answer 4

a measure of risk

Question 5

What is incidence rate?

Answer 5

incidence rate - rate at which susceptible individuals become infected per unit time

Question 6

What is prevalence?

Answer 6

proportion of individuals in the populations that have the outcome of interest at any given time

Question 7

What is prevalence a measure of?

Answer 7

measure of burden like taking a slice through the population at any time

Question 8

What are the challenges with prevalence?

Answer 8

similar challenges as incidence - numerator (who is really infected) denominator (who is actually at risk)

Question 9

What is point prevalence?

Answer 9

point prevalence-current cases

Question 10

What is period prevalence?

Answer 10

period prevalence - current cases over a specified period of time

Question 11

What is the relationship between prevalence and incidence?

Answer 11

Prevalence = incidence * duration of the disease

Question 12

What is relative risk?

Answer 12

relative risk- the ratio of the risk of disease in exposed individuals to the risk of disease in unexposed individuals - measures the association between exposure and disease

Question 13

What do the values of RR mean?

Answer 13

• RR =1 - no association
• RR >1 - positive association exposed are more likely to get the disease
• RR <1 - negative association - unexposed are more at risk

Question 14

What is odds ratio?

Answer 14

odds ration - ration of odds of exposure in diseased vs odds of exposure in non-diseased group

Question 15

What is transmission?

Answer 15

passing from an infected individual or group to a different individual or group weather the other individual was previously infected

Question 16

What is a secondary attack?

Answer 16

secondary attack rate - proportion of individual affected individuals infected amongst susceptible hosts in contact with a primary case

Question 17

Why is there a discrepancy between what we can readily observe and the disease process

Answer 17

There is a discrepancy between what we can readily observe and the disease process. An individual can be infectious before they have clinical symptoms

Question 18

How do you calculate incidence rate?

Answer 18

of new cases of a disease occurring during a specified period of time/sum of different times that each individual was at risk

Question 19

how to calculate point prevalence?

Answer 19

(# of cases at a specified point in time/ population at the specified point in time) * 100

Question 20

What is the formula for relative risk?

Answer 20

incidence in exposed group / incidence in unexposed group

Question 21

Relative risk calculation from table

Answer 21

see notes

Question 22

what is the formula for odds ratio?

Answer 22

odds of exposure in exposed group / odds of exposure in disease free group

Question 23

calculation of odds ratio from table

Answer 23

see notes

Question 24

what is the formula for secondary attack rate?

Answer 24

of new cases of a disease occurring among primary contact / # total number of contacts