SpPin and SnNout

To understand what is meant by the terms SpPin and SnNout, we need to understand the notions of sensitivity and specificity.

SpPin

When a sign, test or symptom has an extremely high specificity (say, over 95%), a positive result tends to rule in the diagnosis. For example, the specificity of 3 or more positive responses on a CAGE questionnaire in diagnosing alcoholism is >99% among internal medicine patients. Therefore, if a person does answer “yes” to 3 or 4 of the CAGE questions, it rules in the diagnosis of alcohol dependency.

SnNout

When a sign, test or symptom has a high sensitivity, a negative result rules out the diagnosis. For example, the sensitivity of the loss of retinal vein pulsation in diagnosing high intracranial pressure is 100 per cent. Therefore, if a person displays retinal vein pulsation, it rules out important increases in intracranial pressure.

These terms are closely related to the measures of:

• Positive Predictive Value: The proportion of people with a positive test who have the target disorder; and
• Negative Predictive ValueThe proportion of people with a negative test who do not have the target disorder.

Often the best place to look for SpPins and SnNouts is at the highest (for SpPins) and lowest (for SnNouts) levels of multilevel likelihood ratios.