Psychometric Properties of Clinical tests

Authors

Affiliations

Nate Yomogida, B.S., SPT

Doctor of Physical Therapy

B.S. in Kinesiology

Chloë Kerstein, B.S., SPT

Doctor of Physical Therapy

B.A. in Neuroscience

Lab Test	If…	What is the chance that…
Sensitivity	The patient has a disease…	…a lab result will be positive?
Power	There is a difference between populations…	…a result will be statistically significant?
Specificity	The patient does not have the disease…	…a lab result will be negative?
1-alpha	There is no difference between populations…	…a result will not be statistically significant?

Understanding Different Psychometrics

Sensitivity & Reliability

Sensitivity and Reliability are used to assess the performance of an alternative test against the gold standard^{monaghanFoundationalStatisticalPrinciples2021a?}

Predictive Values

• PPV and NPV reflect the proportion of positive and negative results that are true positives and true negatives¹.
• PPV answers the question: “if I have a positive test, what is the probability that I actually have the disease?”¹
• NPV answers the question: “if I have a negative test, what is the probability that I actually don’t have the disease?”¹

\[ \textrm{PPV} = \frac{\textrm{True Positives}}{\textrm{Test Positives}} = \frac{\textrm{True Positives}}{\textrm{True Positives} + \textrm{Test Positives}} \]

\[ \textrm{NPV} = \frac{\textrm{True Negatives}}{\textrm{Test Negatives}} = \frac{\textrm{True Negatives}}{\textrm{True Negatives} + \textrm{Test Negatives}} \]

What makes Predictive values unique?

• Unlike sens/specificity, PPV and NPV depend on the pre-test probability (determined by baseline risk factors)

(i.e., probability of the presence of the disease before a diagnostic test), which is determined by baseline risk factors such as disease prevalence

References

1.

Monaghan TF, Rahman SN, Agudelo CW, et al. Foundational Statistical Principles in Medical Research: Sensitivity, Specificity, Positive Predictive Value, and Negative Predictive Value. Medicina (Kaunas, Lithuania). 2021;57(5):503. doi:10.3390/medicina57050503