Free-Cog revisited: the diagnostic contribution of cognitive and executive function.

Aim: To examine Free-Cog, a recently described, hybrid screening instrument, as separate tests of cognitive (Free-Cog-Cog) and executive function (Free-Cog-Exec) to see if this improved screening accuracy for cognitive impairment compared with standard Free-Cog. Materials & methods: Free-Cog-Cog and Free-Cog-Exec were combined using Boolean logical 'AND' and 'OR' operators (serial and parallel combination), and also used to construct a stepwise decision tree. Results: Serial combination improved specificity and positive predictive value whereas parallel combination improved sensitivity, typical findings with these operators. Stepwise application identified groups with high and low probability of cognitive impairment but failed to differentiate adequately those in the intermediate uncertain diagnosis group. Conclusion: Study findings suggest limited benefit from reformulations of Free-Cog compared with the standard instrument.