Figure 3.

Frequency of concept phrases annotated as Problem. The horizontal axis represents distinctive Problem phrases ranked from 1 to 6009 by their frequencies. The bar graphs show the frequencies of each phrases in log₂ scale (left vertical axis) and the line graph shows the cumulative percentage of phrase frequency over all Problem phrase occurrences (left vertical axis). The phrase ranked first is ‘hypertension.’ It is annotated 147 times, which constitutes 1.2% of all Problem phrase occurrences (11 968). Nearly 80% of Problem phrases appear only once in the corpus.