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20 Cards in this Set
- Front
- Back
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What is the purpose of herd level testing?
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determine if the herd is positive or negative for a disease
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What is a herd level test?
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evaluation of a sample (or all) of the animals in a herd to classify the herd as positive or negative
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Are pooled samples from different herds classified as a herd level test?
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No, because it isn't specific for one particular herd then
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What is herd level sensitivity?
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the probability that a positive herd gives a positive test result
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What is herd level specificity?
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the probability that a negative herd gives a negative test result
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What are herd level sensitivity and specificity dependent on?
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number of animals tested
true prevalence in the herd herd cutoff value for positive/negative diagnostic sensitivity and specificity |
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What is a herd level PPV and herd level NPV?
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HPPV is the probability that a test positive herd is truly positive
HNPV is the probability that a test negative herd is truly negative |
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What is the purpose of sampling?
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provide an unbiased estimate of the variable being investigated in the population
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What is a target population?
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population to which the test results of a sample will be extrapolated
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Why is random sampling important?
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allows inferences to be made about the entire herd or population based on the tests of some individuals
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What is simple random sampling?
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all animals are included, and a random number generator or similar technique is used to choose which animals to sample
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What is systematic random sampling?
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The first animal sampled is random, then every nth animal is sampled
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What is a disadvantage of systematic random sampling?
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some animals may not be included because they don't go through the chute etc
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What is stratified random sampling?
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samples of subgroups within a herd are chosen based on what portion of the total they represent
*use simple random sampling within each subgroup |
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What are the major types of non-random sampling?
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haphazard
convenience targeted |
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What type of sample should be used to estimate prevalence?
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random sample
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What type of sample should be used to determine the presence of a disease?
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random or targeted sample
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What things are required to estimate prevalence in a herd?
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max tolerable error of the estimate
reliability coefficient true prevalence estimate test accuracy (Se, Sp) |
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What is the maximum tolerable error?
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how large of an error one is willing to allow in the prevalence estimate
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How would you adjust the sample size needed if the herd is finite?
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alter denominator
use the adjustment when n>0.05N |
