Table 2 Comparison of common Level 1 BCI-based AAC performance metrics

Accuracy/Error Rate

Acc = P; Err = (1 - P)

Cohen’s Kappa

$\kappa =\frac{P-1/N}{1-1/N}$

Confusion Matrix

A matrix with intended (true) outputs as rows, actual outputs as columns, and the number of occurrences in the intersections.

IMutual Information or the formulation in[97]

$I\left(X;Y\right)={\displaystyle \sum _Y{\displaystyle \sum _{X}p\left(x,y\right)\times log\left(\frac{p\left(x,y\right)}{p\left(x\right)*p\left(y\right)}\right)}}$

(Note this can be used to measure throughput rate by simply dividing by the time per trial)

Information Transfer Rate (ITR)

$\mathit{ITR}=\frac{1}{c}\left({log}_2\left(N\right)+P{log}_2\left(P\right)+\left(1-P\right){log}_2\left(\frac{1-P}{N-1}\right)\right)$