An alternative scheme for perplexity estimation

Language models are usually evaluated on test texts using the perplexity derived directly from the model likelihood function. In order to use this measure in the framework of a comparative evaluation campaign, we have developped an alternative scheme for perplexity estimation. The method is derived from the Shannon game and based on a gambling approach on the next word to come in a truncated sentence. We also use entropy bounds proposed by Shannon and based on the rank of the correct answer, in order to estimate a perplexity interval for non-probabilistic language models. The relevance of the approach is assessed on an example.