Free-Cog reformulated: analyses as independent or stepwise tests of cognitive and executive function

Abstract

Free-Cog is a recently described, hybrid screening instrument incorporating tests of cognitive and executive function. In this study, Free-Cog was reformulated as separate tests of cognitive function and executive function to examine whether this might improve screening accuracy for cognitive impairment (dementia and mild cognitive impairment) compared to the standard, unitary Free-Cog. The two separate tests, designated Free-Cog-Cog and Free-Cog-Exec, were either combined using the Boolean logical AND and OR operators (serial and parallel combination) or used to construct a stepwise decision tree. Serial combination improved specificity and positive predictive value whereas parallel combination improved sensitivity, findings typically observed when applying these operators. Stepwise application identified groups with high and low probability of cognitive impairment but failed to adequately differentiate those in the intermediate uncertain diagnosis group. Although the dataset used was relatively small, the findings of this study suggest little benefit for reformulations of Free-Cog compared to the standard, unitary instrument.

Cognitive Screening in Older People Using Free-Cog and Mini-Addenbrooke’s Cognitive Examination (MACE)

“…This is the combination of outcomes that would be desirable for a screening test for cognitive impairment in older patient cohorts. This outcome might possibly reflect the hybrid nature of Free-Cog as a test of both cognitive and executive functions, since other studies have suggested such a combination may improve detection of neurocognitive disorder [20], although fragmenting the Free-Cog into separate tests of cognitive and executive functions did not suggest better overall performance than the unitary Free-Cog [16]. Other analyses of Free-Cog have previously shown that it fares well in comparison to other short cognitive screening instruments in so-called "metrics of limitation" such as misclassification rate and net harm/net benefit ratio [21].…”

“…Free-Cog is a hybrid screening instrument of cognition and executive function (item content shown in Table 1, left hand column), purposely designed to have a conversational quality in order to put patients at their ease and hence maximise performance [10]. Free-Cog was used in its standard, unitary formulation, rather than as separate cognitive and executive function tests formulated either sequentially using Boolean logical operators or as a stepwise decision tree, as examined elsewhere [16]. MACE (item content shown in Table 1, right hand column) is a brief cognitive screening instrument derived from the longer Addenbrooke's Cognitive Examination in its third iteration, ACE-III [17].…”