Table 2. Hearing thresholds as absolute values and Z-scores (with 95% CI): 15 year follow up (n = 35, mean age 37.5, SD 3.2 years). Statistically significant values have been marked with an asterisk. * P < 0.05, ** P < 0.01, *** P < 0.001 .

Frequency	Left		Right
	dB (95% CI) delta	Z-score (95% CI) delta	dB (95% CI) delta	Z-score (95% CI) delta
250 Hz	1.2 (-5.1–7.5) -3.7 **	0.15 (-1.39–0.15) -0.47	1 (-4.1–6.1) -2.6*	0.05 (-1.19–1.29) -0.43
500 Hz	1.4 (-6.3–9.1) - 4.5 **	0.11 (-1.66–0.11) -0.75*	1 (-5.2–7.2) -5.8***	0.02 (-1.36–1.4) -1.07***
1 Hz	5 (-2.1–12.1) -0.5	0.68 (-0.77–0.68) -0.2	2.4 (-3.1–7.9) -4.6***	0.2 (-0.94–1.34) -0.96***
2 Hz	5.6 (-3.6–14.8) -1.7	0.48 (-1.24–0.48) -0.86**	4 (-2.8–10.8) -2.7**	0.25 (-1.03–1.53) - 0.96***
3 Hz	8.7 (-3.4–20.8) +1.6	0.78 (-1.19–0.78) -0.46	4 (-6.3–14.3) 0.7	-0.04 (-1.79–1.71) -0.82***
4 Hz	9.7 (-1.7–21.1) -0.9	0.71 (-0.92–0.71) -1.11***	7.6 (-4.6–19.8) +0.4	0.34 (-1.45–2.13) -0.86**
6 Hz	17.1 (3.7–30.5) +12 ***	1.33 (-0.31–1.33) +0.66	15.6 (2.2–29) +9.3***	1.11 (-0.52–2.74) +0.21
8 Hz	4.7 (-5–14.4) 0	-0.26 (-1.42–0.9) -0.77**	5.3 (-5.5–16.1) -0.2*	-0.22 (-1.45–1.01) -0.95**