Relationship between prevalence and MHI-5 and MCS cutpoints for four optimisation methods. 1. Case prevalence is altered by varying the cutpoint used to define caseness on the GHQ-12 from 1 to 12. 2. Solid line denotes the Youden Index. 3. Dashed line denotes the (0,1) method. 4. Dotted line denotes the minimising the error rate method. 5. Dashed and dotted line denotes the prevalence matching method. 6. The minimax method is excluded since it is predominantly coincidental with the prevalence matching method.