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