Regarding question F4. CALFRAST part b. Is the question asking us to calculate the prior probability of the patient taking as reference the subject's self-assessment of hearing or should we include the self-assessment as if it was another result added to Strong and Faint?
Thank you
Thank you for posting on the forum.
The question is asking you to calculate the prior or pre-CALFRAST probability based on the patient's self-assessment. The patient's self assessment is NOT to be treated as another result on the CALFRAST. The CALFRAST has 3 possible results. From most to least abnormal: 1) Cannot hear strong stimulus; 2) Can hear strong but not weak; 3) Can hear weak.
Best,
MAK
There has been an additional question about F4. CALFRAST on the final exam.
You do not need to understand the gold standard audiometry that determined whether the patient had hearing impairment or not; just assume that it is valid. Of all the 442 subjects in the study, 151 had hearing impairment and 291 didn't have hearing impairment.
The single multi-level test was done on all of the subjects in the sample, Not being able to hear the stimulus is a "positive" test. At the higher threshold, 61% of patients with hearing impairment had a positive test. At the lower threshold 99% of patients with hearing impairment had a positive test. That is enough to do the problem.
Some of you are confused by the note that instructs you to use the percentages, not the counts. We added that note because the authors made an error. The "FN = 59" should have been "FN=61". There were actually 61 not 59 subjects with hearing impairment who could hear the strong stimulus. This means that the sensitivity of "Strong Stimulus" to identify hearing impairment was actually 90/151, not 90/149. Either way, the sensitivity of the test at the higher threshold is 60%, not 61%. This slight error is perpetuated in the table. We instructed you to use the percentages, but if you prefer to use the counts, just correct the "FN=59" to "FN=61", and you will get full credit if you do the remainder of the problem correctly.
Regarding (b), as per my prior post, the patient's self assessment of hearing is not part of the CALFRAST. You should use the patient's self assessment of hearing to establish a pre-CALFRAST probability of hearing impairment.
