Table 3. Hearing thresholds as absolute values and Z-scores (with 95% CI): 20 year follow up (n = 21, mean age 41.9, SD 2.6 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	4.3 (-3.5–12.1) -1.9	0.88 (-0.99–0.88) -0.04	4.1 (-3.1–11.3) +0.2	0.87 (-0.99–2.73) +0.32
500 Hz	2.4 (-5.8–10.6) -4*	0.28 (-1.59–0.28) -0.65	1.4 (-4.1–6.9) -5.3***	0.03 (-1.22–1.28) -1.07***
1 Hz	5.5 (-4.2–15.2) -0.9	0.64 (-1.35–0.64) -0.43	3.1 (-2.5–8.7) -4.0*	0.15 (-1–1.3) -1.02
2 Hz	6.2 (-3.4–15.8) -1.2	0.22 (-1.47–0.22) -1.11**	2.4 (-5.3–10.1) -3.8**	-0.34 (-1.79–1.11) -1.44***
3 Hz	11.9 (-3.5–27.3) +4.8*	0.95 (-1.37–0.95) -0.3	4.5 (-7.3–16.3) +1.7	-0.19 (-2.07–1.69) -0.63
4 Hz	11.9 (-2.1–25.9) +1.3	0.43 (-1.51–0.43) -1.4**	10 (-5.1–25.1) +3.1	0.16 (-1.94–2.26) -1.01 *
6 Hz	18.1 (4.8–31.4) +12.2**	0.80 (- 0.73–0.8) -0.05	16.2 (4.9–27.5) +8.8**	0.64 (-0.68–1.96) -0.49
8 Hz	9.8 (-3.5–23.1) +4.1	-0.10 (-1.54–1.34) -0.73*	6.4 (-4.7–17.5) +1.6	-0.54 (-1.85–0.77) -1.13**