When we do this, however, we lose substantial information.
Common sense says that the first patient is much more likely to be hypothyroid than the second.
But, using sensitivity and specificity numbers based on normal versus abnormal, we get the same posttest probabilities. The likelihood ratio method can take into account test results at multiple different levels of severity. They measured T4 and TSH values in ambulatory patients with suspected hypothyroidism and used the TSH values as a gold standard for determining which patients were truly hypothyroid. Further, the lower the T4 value, the more likely the patients are to be hypothyroid. Values near one indicate a result that does not substantially change disease likelihood.