Sensitivity vs Specificity – I’m POSITIVE I will never get a research question wrong again!

With another practice board exam behind me, I’m starting narrow in areas that I am consistently trip me up. While there are several areas that still need tuning up, there is one thing in particular that I decided I am just DONE mixing up:

SPECIFICITY vs SENSITIVITY

when considering the validity of a diagnostic test.

Consider this question:

Members of a health task force evaluate a proposal for a new adolescent screening program. The validity of the screening insturment is brought to question. Which measure of validity examines the instrument’s ability to identify diseased persons by comparing true positives?

  1. Adaptability
  2. Selectivity
  3. Sensitivity
  4. Specificity

What did you think? Did you say #3: Sensitivity? Lets break it down:

  • Sensitivity: Is a measure of validity based on the probability that a screening test will be POSITIVE in someone with the disease or target condition (true positives).
  • Specificity: Is a measure of validity based on the probability that a screening test will be NEGATIVE in someone who does NOT have the disease or target condition (true negatives)

So check this out:

sensvsspec

A little way for me to remember…

You can also make your self a little table:

3214

The top left representing SENSITIVITY (two Ts or positives)

The bottom right representing SPECIFICITY (two – or negatives)

Ok, so give this question a try. A little different approach:

If the forced expiratory volume in one second (FEV1) test is negative for airway obstruction in 99% of individuals without lung disease, the the measurement of FEV1 is:

  1. Sensitive
  2. Specific
  3. Reliable
  4. Valid

Did you recognize that the question is asking about TRUE NEGATIVES? That is right! The test has high SPECIFICITY (two – ) or #2 !

Go forth and concur those research questions friends!

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