700
edits
Changes
no edit summary
==Prevalence==
==Prevalence==
The prevalence of a disease is the proportion of animals in the population of interest which are 'diseased' at any specific point in time. This may be a single point (in which case, the measure is the '''point prevalence'''), or may be over a period (in which case the '''period prevalence''' is given). However, it is important to realise that this measure will therefore include both old and new cases of disease, which can be a problem when attempting to investigate risk factors for a disease of long duration (as many of the diseased animals are likely to have had the disease for some time). The prevalence can be viewed at an individual animal level as the 'probability that an animal selected at random from the population will be diseased'. The prevalence of disease is commonly obtained from [[Study design#Surveys|surveys]] or cross sectional studies, although in some cases, it can be estimated from a cohort study.
The prevalence (also known as the ''prevalence risk''') of a disease is the proportion of animals in the population of interest which are 'diseased' at any specific point in time. This may be a single point (in which case, the measure is the '''point prevalence'''), or may be over a period (in which case the '''period prevalence''' is given). However, it is important to realise that this measure will therefore include both old and new cases of disease, which can be a problem when attempting to investigate risk factors for a disease of long duration (as many of the diseased animals are likely to have had the disease for some time). The prevalence can be viewed at an individual animal level as the 'probability that an animal selected at random from the population will be diseased'. The prevalence of disease is commonly obtained from [[Study design#Surveys|surveys]] or [[Study design#Cross sectional studies|cross sectional studies]], although in some cases, [[Study design#Cohort studies|cohort studies]] may be appropriate (dependent on how animals were selected).
==Incidence==
==Incidence==
The incidence of disease describes the frequency of new cases of disease amongst
The incidence of disease describes the frequency of new cases of disease amongst previously nondiseased animals, and there are two main methods of measuring it - known as the '''incidence risk''' and the '''incidence rate'''.
===Incidence risk===
The incidence risk (also known as the ''cumulative incidence''') is the proportion of nondiseased animals which develop disease over a particular period of time, and so only relates to the period of time in question (meaning that this period must always be stated along with the risk estimate).
===Incidence rate===
==Time to event==
==Time to event==