3 ms·

Hmm. So that looks like two separate issues to me, but maybe I'm missing something. I see: 1. Additional always-present criterion of distress 2. Knowledge of

Hmm. So that looks like two separate issues to me, but maybe I'm missing something. I see: 1. Additional always-present criterion of distress 2. Knowledge of prior base rates as a means of estimating a proportion of false positives. The first one makes sense to me in connection with the earlier comment. We aren't great at definitively reading our own states: it's easy for us to imagine symptoms, especially when prompted. But if something is actually wrong, an element of distress is typically present. The second one seems like a separate issues though, or at least I don't see the connection. It seems like there are two important bits of information for correcting false positives. The first is that you have a known accuracy which suggests a 1 in 1000 chance of any diagnosis being incorrect; the second is that through historical record you can estimate how many people in e.g. the US are having a hard attack at any given moment on average. I don't see the connection between either of those pieces of information and loose diagnostic criteria though.

cortesoft 6y ago
The base rate part is just explaining why the diagnostic doesn't work when applied on a healthy population (like med students) The instruction would be something like "if the patient complains of x, check for symptom y... if the have symptom y, they are likely suffering from z" But the med student then checks themselves for symptom y, and thinks they have z, but that is only the case if they are suffering from x. The suffering from x part is what changes the base rate, and can't be ignored.
- westoncb 6y ago
  But in the patient's complaint about X, wouldn't X just be another symptom? For instance, let's say a patient complains of a headache. The doctor uses whatever other knowledge they have of the patient to come up with some candidate diagnoses, and proceeds checking for symptoms from each of the candidates. Presumably 'headache' is just another symptom on the diagnostic criteria for each of the other candidates. So why is it treated specially? (Btw, thanks for your response—not sure why you were downvoted, but that was not from me!)
  - cortesoft 6y ago
    Right, my point is that the symptom X is often an implied one.... it isn't expressed in the diagnostic test explicitly, because the diagnostic test is run only when someone has symptom x.

cortesoft 6y ago

The base rate part is just explaining why the diagnostic doesn't work when applied on a healthy population (like med students) The instruction would be something like "if the patient complains of x, check for symptom y... if the have symptom y, they are likely suffering from z" But the med student then checks themselves for symptom y, and thinks they have z, but that is only the case if they are suffering from x. The suffering from x part is what changes the base rate, and can't be ignored.

westoncb 6y ago
But in the patient's complaint about X, wouldn't X just be another symptom? For instance, let's say a patient complains of a headache. The doctor uses whatever other knowledge they have of the patient to come up with some candidate diagnoses, and proceeds checking for symptoms from each of the candidates. Presumably 'headache' is just another symptom on the diagnostic criteria for each of the other candidates. So why is it treated specially? (Btw, thanks for your response—not sure why you were downvoted, but that was not from me!)
- cortesoft 6y ago
  Right, my point is that the symptom X is often an implied one.... it isn't expressed in the diagnostic test explicitly, because the diagnostic test is run only when someone has symptom x.