Can an average of thresholds at 2 kHz and 4 kHz substitute for the threshold at 3 kHz in pure tone audiometry? A study based on the Korean National Health and Nutrition Examination Survey 2010–2012

BACKGROUND: When evaluating hearing disability in medicolegal cases, an average of thresholds at several frequencies is calculated using pure tone audiometry. Occasionally, there are instances in which thresholds at certain frequencies are omitted. One typical example is the threshold at 3 kHz (H3k). The American Academy of Otolaryngology–Head and Neck Surgery Committee on Hearing and Equilibrium (1995) suggested that the average of thresholds at 2 kHz and 4 kHz (H24k) could replace H3k for a comparison of results between studies. However, to the best of our knowledge, there is no report in the literature that compares H3k and H24k. OBJECTIVE: This study aimed to investigate the agreement between H3k and H24k. METHODS: This study is based on the Korea National Health and Nutrition Examination Survey (KNHANES) 2010–2012, which was conducted by the Korean government. A total of 18,472 participants (unweighted) who represented 39,357,497 Koreans (weighted) were included. To verify the agreement of H3k and H24k, a paired t-test, Cohen’s d, Pearson’s correlation, Cronbach’s coefficient, intraclass correlation coefficient (ICC), a Bland–Altman plot, and linear regression analysis were used. RESULTS: The means of H3k and H24k were 16.2 dBHL and 16.6 dBHL, respectively. They were significantly different in a paired t-test (p<0.0001), which resulted from the large sample size. In contrast, the effect size (Cohen’s d) was 0.02, which meant that the two groups nearly overlapped. The means showed strong correlation: Pearson’s correlation coefficient = 0.92, Cronbach’s alpha = 0.96, and ICC = 0.92. A strong linear predictive relationship between H3k and H24k was found: y = –0.6821 + 1.0186x, where x = H24k, y = H3k, and p<0.0001. However, the Bland–Altman plot showed large upper and lower limits of agreement (LOA) of 15.0 dBHL and –15.8 dBHL, respectively. Irrespective of age and degree of the four-tone average (0.5, 1, 2, and 3 kHz) hearing loss or thresholds at 2 kHz, 3 kHz, and 4 kHz, the absolute LOAs were greater than 10 dBHL. CONCLUSIONS: Despite a very strong correlation between the two thresholds, H3k and H24k showed clinically large LOAs. Therefore, it would be improper to substitute H24k for H3k in an individual requesting a hearing disability rating. However, since the overall means of the H3k and H24k samples were nearly equal, H24k can replace H3k for a mean comparison of results between studies. This result supports the 1995 Committee on Hearing and Equilibrium guideline.