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

Metric Description/Equation Evaluation criteria
Throughput Categorical outputs Unbiased Practicality
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 $I\left(X;Y\right)=\sum _{Y}\sum _{X}p\left(x,y\right)×log\left(\frac{p\left(x,y\right)}{p\left(x\right)*p\left(y\right)}\right)$
(Note this can be used to measure throughput rate by simply dividing by the time per trial)

Information Transfer Rate (ITR) $\mathit{ITR}=\frac{1}{c}\left({log}_{2}\left(N\right)+P{log}_{2}\left(P\right)+\left(1-P\right){log}_{2}\left(\frac{1-P}{N-1}\right)\right)$
1. P: probability of correct selection; N: number of choices; p(x): marginal distribution of X; p(x,y): joint distribution of X and Y; c: time per selection.
2. Check marks indicate that the metric fulfills the evaluation criterion. 