Assumptions: The rates shown at each level for each group are constant.
Requirements:
(1) Study groups large enough to provide reliable estimates.
(2) Intervals defined to allow for optimum resolution.
percent of people in study group showing a value in a given range =
= (number of people showing value within range) / (total group size) * 100%
This can be transported to a general population based on the prevalence of the disease.
number of people with disease =
= (prevalence in percent) * (population size)
number of people without disease =
= (population size) – (patients with disease) =
= (100% - (prevalence)) * population size
number of people with disease in general population expected to show a result in a given range =
= (percent of people with disease in study population showing a value in a given range) * (number of people with disease)
number of people without disease in general population expected to show a result in a given range =
= (percent of people without disease in study population showing a value in a given range) * (number of people without disease)
percent of people with a result in a given range who have the disease =
= (number expected with disease) / ((number expected with disease) + (number expected without disease)) * 100%
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percent of people in given range (category) with disease
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Interpretation of Result Relative to Diagnosis
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100%
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patient diseased (diagnostic)
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> 80%
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patient probably diseased (supports)
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20 – 80%
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patient may or may not have disease (not informative)
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< 20%
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patient probably not diseased (does not support)
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0%
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patient not diseased (excludes the diagnosis)
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