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For the stroke case about the 56 y/o female who fell in the bathroom at work, there is a question about sensitivity and specificity related to PASS score?
The correct answer states “high confidence the patient will be independently ambulatory upon discharge from IP rehabilitation due to high sensitivity of the PASS”
However, in the question lead, the specificity was as higher percentage than sensitivity and the last sentence of the exam answer explanation states “Therefore, because this patient’s test results were positive >12.5/36, we are confident that the patient will be independently ambulatory due to the specificity of PASS.”
So, why is the answer not “high confidence the patient will be independently ambulatory upon discharge from IP rehabilitation due to high specificity of the PASS”?
Thank you!
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Hi Holly! The PASS has a fairly high sensitivity and specificity. Sensitivity, however, is the true positive rate – or the likelihood that the score will be positive (above the cut-off) given the person has the condition (future independence with ambulation). Specificity is the true negative rate.
Highly sensitive tests are most useful for ruling IN conditions if the test result is positive. Highly specific tests are most useful for ruling OUT conditions if test results are negative. Therefore, because this patient’s test result was positive (>12.5/36), we are confident that the patient will be independently ambulatory due to the specificity of the PASS.
Sensitivity and specificity are tricky and I need to re-teach myself every time it comes up!
Here are a couple threads from our PCS Advantage forums that discuss sensitivity and specificity a little further that might be helpful. If you search in the forums, you can find other threads where the topic is discussed – and one of us might have found a way to explain it that makes the most sense to you!
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Hi Chrissy: Your answer here is still confusing to me. You state that “we are confident the patient will be independently ambulatory due to the
high specificity of the PASS”, but the correct answer indicated on the quiz says it is due to the high sensitivity of the PASS. These answers seem contradictory. Based on the explanation of sensitivity vs specificity, sensitivity makes sense, but your answer to the question and the explanation in the quiz states specificity. Can you please clarify? Thank you! -
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It looks like the typo has been fixed in the explanation to read ‘due to the sensitivity of the PASS’. The reason we are positive she will be independent based on sensitivity and not specificity, even though specificity is higher is because of what they are testing. Specificity is for ruling out conditions whereas sensitivity is for ruling in. If the specificity is high and the test says something is NOT going to happen, then we are confident it is a true negative and we trust the outcome WON’T happen. If the sensitivity is high and the test says something IS going to happen, then we are confident that is it a true positive and we trust the outcome WILL happen. The results of her score puts her in the range of being independent so we are looking to see if we can trust that it will happen, aka is this a true positive, which is sensitivity. If the score was in the range that she would not be ambulatory, then the high specificity would be the best indicator to determine if she would or would not be ambulatory, because we are trying to determine if it is a true negative result. In that scenario, a high specificity would give us high confidence that she would not be independently ambulatory upon discharge based on her PASS score.
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