Exam 1: Measures of Frequency Prevalence Flashcards
What is prevalence?
Proportion of animals within a population that have a condition of interest within the time of interest/within the study period
How do you calculate prevalence?
Number of cases / Total number of animals measured
What is point prevalence?
Prevalence at a given moment in time, generally the default understanding of prevalence
What is period prevalence?
Number of cases identified over a period of time
What is the relationship between prevalence and incidence?
Prevalence = incidence x duration
What is the prevalence of disease with long duration?
High as long as they are not fatal
What is the prevalence of a disease that has a very short duration or is highly fatal?
It will have a prevalence near 0
What is incidence the probability of?
Becoming a case
What is prevalence the probability of?
Being a case
Describe incidence
Measures the disease force
Useful when assessing primary control measures
Useful to evaluate biosecurity/infection control
Describe prevalence
Useful to assess the amount of effort needed
Can be altered if effective treatments are given and life is prolonged but disease is still present
Says nothing about the number of new cases, or change in disease force
Describe rates (incidence density)
Have time in the denominator
Apply to a group
Are scientifically precise
Describe cumulative incidence (risk)
Expressed as proportion
Applies to a group or individual
Commonly used, may not account for withdrawals
When should you standardize?
When cumulative incidence is used
When desire to compare risk between 2 groups
When the desire to compare overall risk
When a confounding risk factor could be in play
What is confounding?
A mixing of effects
