Development and Evaluation of Automotive Speech Interfaces: Useful Information from the Human Factors and the Related Literature

Table 10

Variables used for evaluating entire systems or system modules.

Module	Variables
Whole system	Task completion time, task completion rate, transaction success, number of interaction problems, query density, concept efficiency
Speech recognition	Word and sentence error rate, vocabulary coverage, perplexity
Speech synthesizer	User perception, speech intelligibility, pleasantness, naturalness
Language understanding	Lexical coverage, grammar coverage, real-time performance, concept accuracy, concept error rate