Lecture 3

Question 1

What are the different epidemiological measures (as mentioned in class)?

Answer 1

• count
• ratio
• -proportion
• –prevalence
• —point prevalence
• —period prevalence
• -rate (crude, adjusted, specific)
• –incidence rate(attack rate)

Question 2

Prevalence

Answer 2

• measures the burden of disease in a population
• can be a snapshot of one point in time(point prevalence) or can be a period of time(period prevalence)
• proportion of existing cases/ total population at risk
• note: prevalence is not a rate

Question 3

Prevalence formula

Answer 3

number of new and existing cases/total population at risk during a given time

Question 4

cumulative incidence

Answer 4

places individual with outcome in the numerator and places those who outcome in the denominator
-underestimates risk because ppl who drop out of get counted as people who didn’t develop disease(didn’t follow up so we don’t know that for sure)

Question 5

How is mortality measured?

Answer 5

• annual mortality rate
• cause-specific death rate
• proportionate mortality
• case-fatality rate

Question 6

annual mortality rate

Answer 6

(total number of deaths from all causes in 1 year/ midyear population)*1000

Question 7

cause-specific death rate

Answer 7

total number of deaths from cause A during specified period of time/population at midpoint of time interval)*1000

Question 8

proportionate mortality

Answer 8

(total number of deaths from cause A/ total number of death for all causes) *100

Question 9

case-fatality

Answer 9

(number of deaths from a specific disease/condition/total number of persons with disease)
-measures severity of disease

Question 10

When does mortality help us determine incidence?

Answer 10

mortality helps us determine incidence only when :

• case fatality rate is high
• duration of disease is short

Question 11

direct age adjustment

Answer 11

use of standard population to standardize/get rid of differences in age between populations being compared
-goal is to make distributions the same for risk factors (ex.age,sex…)

Question 12

indirect age adjustment

Answer 12

use when numbers of deaths for each age-specific stratum is not available

• used to compare mortality or morbidity experience of persons in certain subgroup to a general population
• calculate SMR

Question 13

SMR

Answer 13

standardized mortality rate

(observed # of deaths/ expected # of deaths per year)*100

Question 14

How do I interpret SMR?

Answer 14

SMR=100 : observed # of deaths = expected # of deaths
SMR>100: observed # of deaths > expected # of deaths
SMR< 100: observed # of deaths < expected # of deaths

Conclusions: based on the observed number of deaths, we can conclude that comparison population has more, less or equal the amount of deaths compared to the expected population

Question 15

How does prevalence relate to incidence and duration?

Based on this relationship, how can we change prevalence?

Answer 15

prevalence = incidence  * duration 
increase prevalence: 
-long term disease with slow death rates 
-increase in incidence 
decrease prevalence: 
-increase number of deaths from disease/outcome 
-rapid cures 
-decrease in  incidence