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Studies (Case-Control studies (Odds ratio (Odds exposed are diseased ÷…
Studies
Case-Control studies
Data from known sick animals compared with known healthy animals selected at random from the same population, in terms of a risk factor.
Useful where incidence is low, for retrospective studies.
Fixed number of cases and decide on case: control ratio. Usually 1:1 - 1:3 but definitely no more than 1:10.
Divide into diseased or not and exposed or not, then work out odds of disease in exposed and unexposed groups.
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Cohort studies
Animals are allocated to specific risk groups (cohorts) and observed to see if they become become ill. Investigator fixes the number in each cohort.
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Cross sectional studies
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Suspect a disease is more common in group A than group B. Randomly select a certain number of individuals without knowing which group they are part of OR whether they have the disease. Then look for clinical signs in all animals.
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