years. Audiometric test records must be retained for the duration of the affected employee's employment. Additionally, employees, former employees, representatives designated by the individual employee and the Assistant Secretary all must have access to these records. Program evaluation Proper program evaluation is important in maintaining the health of hearing conservation program. The National Institute for Occupational Safety and Health (NIOSH) has created a checklist to help evaluate the effectiveness of a hearing conservation program. It can be found on their website. NIOSH recommends that fewer than 5% of exposed employees should have a 15 dB significant threshold shift in the same ear and same frequency. It also suggests using the term hearing loss prevention program rather than a hearing conservation program. While this change may seem superfluous, it is important to note the advancement. "Conservation" implies a response by the workplace caused by initial signs of employee hearing loss, whereas "prevention" promotes policies (such as "buy quiet") and procedures (such as hearing protection training and education) to decrease the possibility of occupational hearing loss from happening in the first place. Best practices Simply having a hearing conservation program (even a program that complies completely with relevant government regulations) is not necessarily sufficient to prevent occupational hearing loss. A 2017 Cochrane review low-quality evidence that stricter legislation might reduce noise levels. Giving workers information on their noise exposure levels by itself was not shown to decrease exposure to noise. Moderate-quality evidence indicated that training in the correct fitting of ear protection has the potential to reduce noise to safer levels in the short term, but long-term evidence on prevention of hearing loss is lacking. External solutions such as proper maintenance of equipment can lead to noise reduction, but further study of this issue under real-life conditions is needed. Other possible solutions include improved enforcement of existing legislation and better implementation of well-designed prevention programs, which have not yet been proven conclusively to be effective. Lack of evidence does not imply lack of effect; further research on the impact of generally-accepted hearing conservation practices is much needed. In the meanwhile, many hearing conservation organizations advocate for "best practices" that go beyond mere compliance in order to more successfully prevent occupational hearing loss. Some of these are discussed below. Buy Quiet The Buy Quiet policy is an easy way to progress towards a safer work environment. Many traditionally noisy tools and machines are