Lecture 5 8/29/24 Flashcards
What aspect of a disease is evaluated using attack rate?
pathogenicity
What aspect of a disease is evaluated using case fatality rate?
virulence
How does mortality rate differ from case fatality rate?
-mortality rate is calculated out of the total population
-case fatality rate is calculated only out of those with the disease
What is an attack rate ratio?
attack rate in exposed/attack rate in unexposed
Why is it important to compare attack/fatality rates between groups?
provides insight into factors that make one group more susceptible to disease than another
When is it recommended to use adjusted attack/fatality rates?
when differences in the distribution of one or more host characteristics occur among the comparison groups
What are the different ways of expressing incidence?
-incidence count
-incidence risk/cumulative incidence
-incidence rate/incidence density
What is the calculation for cumulative incidence?
animals experiencing event during time/(initial NAR - 1/2 withdrawals during time)
What is required when calculating an incidence rate?
measurement of the follow-up time for each individual in the cohort
What is the calculation for incidence rate?
onsets/sum of person-time @ risk
How do incidence and prevalence relate when incidence and mortality/recovery rates remain constant?
prevalence = incidence x duration of disease
How do incidence and prevalence relate if incidence changes and mortality/recovery remain constant?
prevalence should change in the same direction as incidence
How do incidence and prevalence relate if mortality/recovery changes and incidence remains the same?
prevalence changes in the opposite direction of mortality/recovery
When is incidence greater than prevalence?
disease with short duration due to recovery or death
When is prevalence greater than incidence?
chronic diseases
