Measures of Frequency Prevalence Flashcards
Prevalence
Proportion of animals within a population that have a condition of interest within the time of interest/within the study period
Prevalence formula
of cases / total # of animals measured
Point prevalence
Prevalence at a given moment in time, generally the default understanding of prevalence
Period prevalence
# of cases identified over a period of time - ex: annual prevalnce
Cross secotional studies
Measure of prevalence as a “cross section” of a population
Prevalence and incidence relationship
Prevalence = incidence x duration
Diseases with long duration have _______ prevalence
High
- only if they are not fatal!
When will incidence change dramatically?
During long duration diseases
- prevalence may not change
What happens to prevalence if a disease has a short duration?
Will be near 0
- ex: anthrax infection
What does prevalence not convey?
The need for follow-up care for those affected with a specific disease
Probability of becoming a case
Incidence
- force of disease within a time window
What are 2 measures of incidence?
- incidence rate (density)
- cumulative incidence (risk)
The probability of being a case
Prevalence
- expressed as a proportion (%)
