How hearing conservation training format impacts personal attenuation ratings in U.S. Marine Corps Training Recruits

Figures & data

Figure 1. Histogram showing initial self-fit (ISF) personal attenuation ratings (PARs) in decibels (dB) achieved (i.e. baseline) for all recruits by percent (n = 798). Note: Not included here are the ISF PAR values of the 23 participants who were excluded. The solid vertical line indicates the study pass-fail criterion level of 25.0 dB.

Figure 2. Study design flow chart. Note. Of the 344 participants who qualified, 341 were randomly assigned a training method. A total of 20 participants were excluded during training for various reasons (e.g., use of an alternate earplug [current n = 2, eHPD n = 5, integrated n = 4], an expert fit PAR value < 25.0 dB [eHPD n = 4, integrated n = 3), and not completing the assigned training [integrated n = 2], which resulted in a data set of 321 participants (i.e., current n = 111, eHPD n = 105, integrated n = 105).

Table 1. Pass/fail rate by training method pre- and post-training.

		ISF		SRF
	n	Pass n (%)	Fail n (%)	Pass n (%)	Fail n (%)
Current	111	0 (0)	111 (100)	56 (50)	55 (50)
eHPD	105	0 (0)	105 (100)	97 (92)	8 (8)
Integrated	105	0 (0)	105 (100)	88 (84)	17 (16)
TOTAL	321	0 (0)	321 (100)	241 (75)	80 (25)

Note. The ISF count does not include the 20 persons who were excluded from final analysis. The “Pass” criterion was a PAR value of 25.0 dB.

Figure 3. Attenuation achieved by participant rank ordered by ISF PAR values. Three figures are provided one for each training format: (A) current (n = 111), (B) eHPD (n = 105), and (C) integrated (n = 105). Note. PAR values obtained for ISF (diamonds), EF (triangles), SRF (circles), target PAR (horizontal dark solid line, 25.0 dB), and earplug NRR (horizontal dashed line, 33.0 dB) are shown. Each vertical line connects the PAR values for an individual participant.

Table 2. Means and standard deviations of measured PAR values and Delta PAR.

	n	ISF	SRF	Delta PAR
Current	111	16.7 (7.3)	25.2 (10.8)	8.5 (11.9)*
eHPD	105	16.4 (7.5)	34.1 (7.2)	17.8 (10.5)
Integrated	105	15.6 (7.9)	33.5 (9.6)	17.9 (12.5)

Note. Delta PAR is the mathematical difference between the SRF PAR and ISF PAR. *Post-hoc analysis revealed that Delta PAR for the current fit-training method was significantly lower than the other two training methods (p < 0.001).