Comparison 5. HPD with ANC vs without ANC (immediate).

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation (dB)	1	4	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.1 Alpha‐200 series with Active Noise Cancelling	1	2	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
1.2 Gentex/Bose Active Noise Cancelling	1	2	Mean Difference (IV, Fixed, 95% CI)	0.0 [0.0, 0.0]
2 TTS at 1 kHz (before exposure ‐ after exposure )	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
3 TTS at 2 kHz (before exposure ‐ after exposure )	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
4 TTS at 4 kHz (before exposure ‐ after exposure )	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
5 TTS at 6 kHz (before exposure ‐ after exposure )	1		Mean Difference (IV, Random, 95% CI)	Subtotals only
6 TTS at 8 kHz (before exposure ‐ after exposure )	1		Mean Difference (IV, Random, 95% CI)	Subtotals only