Comparison 2. HPD (muffs) with instructions vs without instructions (immediate) ‐ RCT.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Noise attenuation at 0.5 kHz (REAT)	1	40	Mean Difference (IV, Random, 95% CI)	2.34 [‐0.85, 5.54]
1.1 Wilson Sound Ban cap	1	20	Mean Difference (IV, Random, 95% CI)	4.1 [‐2.47, 10.67]
1.2 Bilsom UF‐1 muff	1	20	Mean Difference (IV, Random, 95% CI)	1.80 [‐1.86, 5.46]
2 Noise attenuation at 1 kHz (REAT)	1	40	Mean Difference (IV, Random, 95% CI)	0.89 [‐3.02, 4.80]
2.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	3.80 [‐3.70, 11.30]
2.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	‐0.20 [‐4.78, 4.38]
3 Noise attenuation at 2 kHz (REAT)	1	40	Mean Difference (IV, Random, 95% CI)	2.57 [‐0.23, 5.38]
3.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	2.70 [‐1.89, 7.29]
3.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	2.5 [‐1.05, 6.05]
4 Noise attenuation at 3 kHz (REAT)	1	40	Mean Difference (IV, Random, 95% CI)	2.23 [0.09, 4.36]
4.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	1.60 [‐3.01, 6.21]
4.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	2.40 [‐0.01, 4.81]
5 Noise attenuation at 4 kHz (REAT)	1	40	Mean Difference (IV, Random, 95% CI)	0.83 [‐3.28, 4.95]
5.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	0.90 [‐6.18, 7.98]
5.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	0.80 [‐4.26, 5.86]
6 Noise attenuation at 6 kHz (REAT)	1	40	Mean Difference (IV, Random, 95% CI)	0.64 [‐3.76, 5.04]
6.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	2.30 [‐7.31, 11.91]
6.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	0.20 [‐4.75, 5.15]
7 Noise attenuation at 8 kHz (REAT)	1	40	Mean Difference (IV, Random, 95% CI)	1.14 [‐3.59, 5.87]
7.1 Wilson Sound Ban Cap	1	20	Mean Difference (IV, Random, 95% CI)	2.0 [‐8.13, 12.13]
7.2 Bilsom UF‐1 Muff	1	20	Mean Difference (IV, Random, 95% CI)	0.90 [‐4.45, 6.25]