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

From: Performance assessment in brain-computer interface-based augmentative and alternative communication

Metric Description/Equation Evaluation criteria
   Throughput Categorical outputs Unbiased Practicality
Accuracy/Error Rate Acc = P; Err = (1 - P)    
Cohen’s Kappa κ = 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 X ; Y = Y X p x , y × log p x , y p x * p y
(Note this can be used to measure throughput rate by simply dividing by the time per trial)
Information Transfer Rate (ITR) ITR = 1 c log 2 N + P log 2 P + 1 P log 2 1 P N 1  
  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.