Step 4: Apply the evidence to your patient
For any given pre-test probability, you can calculate a post-test probability.
Sources of information to determine the pre-test probabilities include: your or another colleague's clinical experience, statistics on frequencies of this disorder in the population, the frequency of the disorder in the study (from the 2x2 Table: (a+c/a+b+c+d = pre-test probability) or another study.
If you know the likelihood ratio positive and likelihood ratio negative, you can use our calculator to determine a post-test probability given any pre-test probability:
Is the diagnostic test available, affordable, accurate, and precise in your setting?