Number Needed (Reciprocal) Measures and Their Combinations as Likelihoods

This chapter considers various “number needed” (reciprocal or multiplicative inverse) measures of test outcome which can be derived from the basic 2 × 2 contingency tableContingency table, as well as certain likelihood measures which may be derived from the “number needed” measures. All of these measures, including some described for the first time here, have been developed to summarise test outcome in a manner which is hopefully more intuitive to clinicians and patients than the traditional measures of discrimination such as sensitivitySensitivity and specificitySpecificity.