1. A method for improving quality of a data processing operation in a plurality of documents, the method comprising the steps of: estimating an error rate for each of at least two fields in the plurality of documents, by sampling a set of documents from among the plurality of documents, wherein the step of estimating an error rate comprises: estimating a probability that data typed for a field in a document is in error, without knowing a correct transcription for the field; and estimating the error rate based at least in part on the estimated probability of error; and identifying a set of critical fields in the plurality of documents based on which fields have error rates higher than a threshold.