Measures of frequency Flashcards
What is a count? What does it not provide information on?
Number of cases in population
No information on size of population
What are proportions?
fractions of the population
What are odds?
Ratio of diseased:non-diseased
What is the rate?
Number of cases over time period
What is incidence?
Frequency of NEW cases during a specific time period
What does incidence not include?
Those already diseased
Incidence requires a clear case definition. Why?
Show that animals were not diseased before
Animals with ‘new’ cases may be recurrent disease
What are the 2 commonly used measures for incidence?
Cumulative incidence
Incidence rate
What is cumulative incidence or incidence risk?
Proportion of disease free animals developing a disease over a time period
What is point and period prevalence?
Point = prevalence at a single point in time Period = prevalence over a time period
What are measures of associations used to determine?
Whether differences in exposure to risk factors are related to incidence
Assess relationship between risk factor and outcome
What can be used to work out methods of assocations?
Relative risk
Odds
Odds ratio
What does measures of association not tell us?
Disease caused by exposure
Frequency of disease
What 2 study designs can be used for measures of association?
Cohort/cross sectional study = frequency of disease in exposed vs non-exposed
Case-control study = frequency of exposure in diseased vs non-diseaesd
What is relative risk?
Risk of disease in exposed individuals compared to risk in non-exposed individuals
