On the Effects of Low-Quality Training Data on Information Extraction from Clinical Reports

In the last five years there has been a flurry of work on information extraction from clinical documents, that is, on algorithms capable of extracting, from the informal and unstructured texts that are generated during everyday clinical practice, mentions of concepts relevant to such practice. Many of these research works are about methods based on supervised learning, that is, methods for training an information extraction system from manually annotated examples. While a lot of work has been devoted to devising learning methods that generate more and more accurate information extractors, no work has been devoted to investigating the effect of the quality of training data on the learning process for the clinical domain. Low quality in training data often derives from the fact that the person who has annotated the data is different from the one against whose judgment the automatically annotated data must be evaluated. In this article, we test the impact of such data quality issues on the accuracy of information extraction systems as applied to the clinical domain. We do this by comparing the accuracy deriving from training data annotated by the authoritative coder (i.e., the one who has also annotated the test data and by whose judgment we must abide) with the accuracy deriving from training data annotated by a different coder, equally expert in the subject matter. The results indicate that, although the disagreement between the two coders (as measured on the training set) is substantial, the difference is (surprisingly enough) not always statistically significant. While the dataset used in the present work originated in a clinical context, the issues we study in this work are of more general interest.