Validity in Screening Tools
Validity refers to the extent to which a tool actually measures a trait. Does the tool actually assess what it purports to measure?
Screening tools should be validated for the targeted population, setting, and disorder or diagnosis.
Importance of validity when selecting a screening tool
Validity is important because validated tools have been proven to measure what they claim to measure in a specific population. A validated tool detects those who truly have the condition.
ADVANTAGES OF VALIDATED TOOL
More likely to get the desired outcomes when using validated tools
as the appropriate persons are targeted
Components of validity
Validity is measured by sensitivity and specificity and by predictive value, which range from 0 – 100%.
Positive and Negative Predictive Values incorporate sensitivity and specificity and are more useful to clinicians because they also consider the population being tested. Ideally, a screening test should be highly sensitive and highly specific and have both positive predictive value and negative predictive value.
The tool should also be reliable or give the same result every time it is used, and it should have high inter-rater reliability when more than one person gives the test.
|Positive predictive value||How many of the subjects who test positive truly have the disease.|
|Negative Predictive Value||How many of the subjects who test negative truly do not have the disease.|
|Reliability||Assures that results obtained by different investigators are consistent when repeated in the same subjects. 11|
Validity of the MNA®
The MNA® is the most well validated screening tool for the elderly. The original validation study on the full MNA® demonstrated the MNA® had a sensitivity of 96%, specificity of 98% and positive predictive value of 97% compared to clinical status. 21 The original MNA®-SF has a sensitivity of 98%, specificity of 100%, and diagnostic accuracy of 99% for predicting undernutrition. 18 The sensitivity and specificity of the recently revised MNA®-SF is almost identical to the original MNA®-SF, confirming the original MNA®-SF is valid and compares well against the full MNA®.420