[All that neurologist would like to know about sensitivity, specificity and predictive values].

The aim of the diagnostic process is to establish the prevalence or probability of a disease given a clinical picture. A diagnostic test could be considered as every piece of information obtained from a patient. Diagnostic test can be done throughout technical devices, medical examinations or questionnaire. The diagnostic test offers information that allows us to classify patients according a different probability to be sick. The operative validity of a test can be done in terms of diagnostic accuracy. It means the ability to truly classify a patient in the right clinical situation. Diagnostic accuracy is the quality of the information provided by a test (sensitivity, specificity). Diagnostic usefulness is the practical value of the provided information. The predictive value of a diagnostic test depends on its accuracy and the prevalence of the disease in the setting where the diagnostic process is to be made. Decision making with the information provided by the test implies to consider the consequences of the false result.