OVER 98% PASS RATE FOR THE NCS, OCS, AND PCS EXAMS › forums › PCS Advantage › Sensitivity vs Specificity
February 24, 2023 at 7:34 pm #489016Alex PolandParticipant
I am confused on a question on exam 2:
24. A standardized assessment that helps identify gross motor delay in children has a sensitivity of 98% and a specificity of 50%. After performing the assessment, the scores indicate that the child has a gross motor delay. How can you interpret this information?
a. The assessment only has a high success rate of correctly identifying children who do not have a gross motor delay
b. The assessment has a high success rate of identifying gross motor delays but may also suggest that there is a gross motor delay when there is not really a delay present
c. The assessment has a high success rate of correctly identifying children who do and do not have a gross motor delay
d. The assessment has a high success rate of identifying children who do not have gross motor delay but may miss some children who actually do have a gross delay
The explanation for the answer is: The sensitivity of a test is the percentage of individuals with a particular condition who are correctly identified as positive by the test. The specificity is the percentage of individuals without a particular condition who are correctly identified as negative by the test. Tests with high sensitivity often have low specificity. They are good for accurately identifying a condition but they also come with a fairly high rate of false positives.
I am confused because in school we learned that for specificity (SPin) when you have a positive value you rule the diagnosis IN versus with sensitivity (SNout) with a negative test you rule the condition out. This seems to be the opposite from what the above explanation is stating. Could someone shed some light on the difference between these two terms? Thanks!
February 24, 2023 at 9:57 pm #489017Jessica LewisParticipant
A confusing topic for sure! Using SPIN and SNOUT when talking about sensitivity and specificity can cause some confusion at times. Often people use the mnemonics SPIN and SNOUT as definitions of specificity and sensitivity, but they and not the definitions. They are mnemonics to remember the RELATIONSHIP of sensitivity and specificity for ruling in and ruling out a diagnosis based on a TEST result.
Sensitivity (true positive rate) is the likelihood that someone with the condition will be positive on the diagnostic test and refers to the percentage of children who are correctly identified as meeting criteria for a condition. This is valuable for confirming a diagnosis and 80% sensitivity is preferable.
Specificity (true negative rate) is the likelihood that someone who does not have the condition will be negative on the diagnostic test and refers to the percentage of children without problems who are correctly identified as such. This is valuable to rule out the presence of a condition and 90% is preferable.
Does this help clear up the confusion?
February 26, 2023 at 7:58 pm #489029Pamela LiangParticipant
I spent quite a bit of time confused about this topic, and honestly I still get confused when I try to read the actual definitions. But one video that was really helpful for me is this one: https://www.youtube.com/watch?v=UsOv0DcXk6w&ab_channel=Physiotutors Hopefully links are allowed to be posted here.
After that, it was easier for me to understand why sensitivity was preferred for screening tools.
Another way to think about it is remembering how COVID tests work: If you get a positive, you definitely have it; if you get a negative, it’s not as conclusive that you don’t have COVID. COVID tests are sensitive, and not as specific.
February 26, 2023 at 8:08 pm #489030Pamela LiangParticipant
So sorry, I swapped the specificity and sensitivity for COVID tests. Most COVID tests are SPECIFIC. But obviously, there are so many of them, some of them may have different psychometrics.
February 27, 2023 at 9:18 am #489032Jessica LewisParticipant
Great resource! Thank you for sharing this Pamela!
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