The EPA requires manufacturers to print a noise reduction rating (NRR) on all non-custom earplugs. The NRR for ER•20s is 12 dB, but actual clinical measurements of properly inserted ER•20s indicate that these earplugs provide almost equal sound reduction (20 dB) at all frequencies in real ears. The required formula used to determine NRR includes an adjustment for individual variability and for those persons who do not wear ear protection as instructed. Many investigators have found no consistent rank order correlation between the real-world NRRs and labeled NRRs. NRR is computed from laboratory data that are not representative of the values attained in the real world by actual users.