Table 5.

Clinical Question 2: Comparison of WDRC versus linear amplification on speech recognition outcomes at low input levels (i.e., < 55 dB).

Citation	Condition	Compression settings	Stimuli	Open/closed set	Presentation level/SNR	Effect size [95% CI]a	p
Christensen (1999)	WDRC	Threshold: low: 45–50 dB SPL Attack time: 5 ms Release time: 50 ms Ratio: variable 1.1:1 to 7.8:1 Volume control: listener unable to adjust during testing	Bisyllabic spondaic words	Open	50 dB SPL/quiet, +5, +10 SNR	NR/NC	ns across SNRs
			Passages	Open	50 dB SPL/quiet, +5, +10 SNR	NR/NC	ns across SNRs
			Sentences	Open	53 dB SPL (40 dB HL)/0, +5, +10, +15 SNR	NR/NC	ns across SNRs
	Linear CL	Threshold: high 75 dB Attack time: 5 ms Release time: adjustable up to 1 s Ratio: 8:1 Volume control: listener unable to adjust during testing
	Linear PC	Threshold: none Attack time: instantaneous Release time: instantaneous Ratio: none Volume control: listener unable to adjust during testing
Gou et al. (2002)	WDRC	Threshold: 40 dB Attack time: NR Release time: NR Ratio: NR Volume control: AGC	Words (discrimination of phonological oppositions)	Closed	40 dB SPL/quiet	NR/NC	p < .001 (favors WDRC)
			Monosyllabic words	Closed	40 dB SPL/quiet	NR/NC	p < .001 (favors WDRC)
			Bisyllabic words	Closed	40 dB SPL/quiet	NR/NC	p < .0001 (favors WDRC)
	Own linear	Threshold: NR Attack time: NR Release time: NR Ratio: NR Volume control: fixed
Jenstad et al. (1999)	WDRC	Threshold: 45 dB Attack time: 10 ms Release time: 200 ms Ratio: varied by DSL prescription Volume control: listener unable to adjust	Nonsense words	Closed	48 dB SPL/quiet (avg. speech at 4 m)	NR/NC	p < .05 (favors WDRC)
			Sentences	Open	48 dB SPL/quiet (avg. speech at 4 m)	NR/NC	ns
	Linear	Threshold: NR Attack time: NR Release time: NR Ratio: NR Volume control: listener unable to adjust
Marriage & Moore (2003)	WDRC	Threshold: 50–55 dB SPL Attack time: 5 ms Release time: 30 ms Ratio: varied between 1.7:1 to 2.7:1 Volume control: NR NR	Words (consonant confusion task) (severe and profound HL)	Closed	60, 50 dBA/quiet, +10 SNR	r = .78 [.07, .97]b	p = .021 (favors WDRC)
			Words (consonant confusion task) (moderate HL)	Closed			Compression × Presentation Level: ns
			Monosyllabic words (severe HL)	Open	55, 45 dBA/quiet, +5 SNR	r = .86 [.16, .98]b	p = .013 (favors WDRC)
			Monosyllabic words (moderate HL)	Open			Compression × Presentation Level: ns
	Linear				60, 50 dBA/quiet, +10 SNR	r = .999b,c	p < .001 (favors WDRC) Compression × Presentation Level: ns
					55, 45 dBA/quiet, +5 SNR	r = .75 [−.16, .97]b	ns Compression × Presentation Level: ns
Marriage et al. (2005)	WDRC	Threshold: 40 dB at 200 Hz; 25 dB at 4400 Hz Attack time: 5 ms Release time: 30 ms Ratio: 1.2:1 to 3.0:1 Volume control: NR	Monosyllabic words (profound HL)	Closed	50 dBA/quiet	NR/NC	p < .01 (WDRC > linear PC) p < .01 (WDRC > linear CL)
			Monosyllabic words (severe HL)	Closed	45 dBA/quiet	NR/NC	ns
			Monosyllabic words (severe HL)	Closed	50 dBA/0 SNR	NR/NC	ns
	Linear CL	Threshold: high Attack time: 0.5 ms Release time: 50 ms Ratio: NR Volume control: NR	Words (profound HL)	Open	50 dBA	NR/NC	ns
			Words (severe HL)	Open	45 dBA/quiet; 50 dBA/0 SNR	NR/NC	ns
	Linear PC	Threshold: high Attack time: 0.5 ms Release time: 5 ms Ratio: NR Volume control: NR
Stelmachowicz et al. (1995)	WDRC	NR	Nonsense syllables	Closed	50 dB SPL	NR/NC	ns
	Linear	NR (conditions assessed using 2 different devices)

Note. avg. = average.

^aPositive effect sizes indicate that the direction of the effect favors WDRC; negative effect sizes indicate that the direction of the effect favors linear amplification.

^bEffect size r calculated using F statistic and degrees of freedom provided in the study.

^cConfidence intervals were not calculable.