1. A method comprising: operating, via a processor of a computing device, a natural language understanding application with a statistical model that generates a sequence of tags assigned to a first sequence of words; developing a first part without human knowledge, the first part being first data used to formulate a replacement statistical model; developing a second part using the human knowledge and annotated words, the second part being a second data used to formulate the replacement statistical model; assigning weighted versions of the first part and the second part to yield the replacement statistical model, wherein the weighted versions are determined based on an amount of annotated data that is available; and during execution of the natural language understanding application in which a second sequences of words is received as speech for processing using the natural language understanding application, assigning, via the processor of the computer device executing the natural language understanding application, a new sequence of tags to the second sequence of words, the new sequence of tags being generated by the replacement statistical model.