Several hearing conservation programs (n=15) from a cross-section of U.S. industries were examined to test whether there are greater rates of change in hearing levels in relation to increasing cumulative noise exposure during the period of audiometric follow-up. The analysis also examined whether rates of hearing loss were lower among workers who wear hearing protection relative to workers who do not. These 15 audiometric databases had a total of 15 794 workers with 62 095 audiograms. Differences in a linear combination of 1--4 kHz biaural hearing levels of consecutive audiometric tests were examined using mixed effects models to account for correlated, repeated observations on individuals. These differences were modeled as a function of cumulative noise, gender, race, hearing protection use, age, learning effects, and baseline hearing level (measured after 14 h of quiet time). Analyses were conducted for the combined and individual databases. The analysis indicates there is significant heterogeneity among the databases. This heterogeneity by database complicates further analysis and makes interpretation of model results difficult. These difficulties will be highlighted with recommendations for data needed to evaluate hearing conservation effectiveness.