Next: Semantic accuracy.
String accuracy measures the distance of the test sentence and the
best sentence. String accuracy is expressed in terms of sentence
accuracy (SA, the proportion of cases in which the test sentence
coincides with the best sentence), and word accuracy (WA). The string
comparison on which word accuracy is based is defined by the minimal
number of substitutions, deletions and insertions of words that is
required to turn the best sentence into the test sentence (Levenshtein
distance). Word accuracy is defined as
where n is the length of the actual utterance and d is the
Levenshtein distance. For example, if the analysis gives 'a b a c d'
for the utterance 'a a c e', then the Levenshtein distance is 2, hence
the WA is 1-2/4 is 50%.