Figure 3c. Graphs show mean Az values (± standard errors) for human observers and two numeric observer models for (a) 3-mm, (b) 6-mm, and (c) 8-mm masses with the compression conditions investigated in this study. Detection of masses was not affected by the image compression ratio, but detection of microcalcifications was decreased at compression ratios of more than 15:1. There was good agreement in detection trends between the numeric observer models and the human observers.