For example there are results for English (Fosler-Lussier & Morgan, 1999) and Japanese (Shinozaki & Furui, 2001) that show that infrequent words are more likely to be misrecognized, which is most likely to be true also for other languages.
in order to improve ASR performance, it is important to understand which factors are most problematic for recognition, identify the types of errors, their main causes and how critical these errors are.