15. An apparatus, comprising: a processor; and a memory coupled to the processor, wherein the memory comprises instructions which, when executed by the processor, cause the processor to: receive a plurality of pre-annotated reference documents; receive a set of annotation types associated with the pre-annotated reference documents; analyze annotation contexts of reference annotations in the plurality of pre-annotated reference documents using the set of annotation types; identify similar annotation contexts between the reference annotations and the set of annotation types; responsive to identifying the similar annotation contexts, cluster the similar annotation contexts thereby forming a plurality of reference annotation clusters; compute a set of reference content heterogeneity scores based on the number of reference annotation clusters for each annotation type in the set of annotation types; compute an integral reference content rate for the set of annotation types; output the integral reference content rate to a user; receive standard performance rates for a text analysis engine; apply the integral reference content rate to the standard performance rates; and generate reliable performance rates for the text analysis engine.
16. The apparatus of claim 15 , wherein the instructions further cause the processor to: compute performance rates for each annotation type in the set of annotation types.