Do hearing protectors protect hearing?

Source: Matthew R. Groenewold, Elizabeth A. Masterson, Christa L. Themann and Rickie R. Davis, American Journal of Industrial Medicine, Volume 57 Issue 9, September 2014
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From the abstract:
Background:
We examined the association between self-reported hearing protection use at work and incidence of hearing shifts over a 5-year period….

Results:
The odds ratio for hearing shift for workers who reported never versus always wearing hearing protection was nonsignificant for OSTS and marginally significant for HFTS. A significant linear trend towards increased risk of HFTS with decreased use of hearing protection was observed.

Conclusion:
The study raises concern about the effectiveness of hearing protection as a substitute for noise control to prevent noise-induced hearing loss in the workplace.