Letter to the Editors
MORE ABOUT HEARING PROTECTOR COMFORT RATINGS
The paper entitled 'An empirical study of comfort afforded by various hearing protection devices: Laboratory versus field results', which recently appeared in Applied Acoustics, Volume 34 (1991), pages 151-179, contained two errors which the authors wish to correct. Both errors involve the field comfort data results, which are discussed beginning on page 166. The errors only involve a minor portion of the text and Fig. 8.
First, as incorrectly stated under the subheading of 'Field comfort index data analysis', the field comfort index (CI) data points did not range from 7 to 49 (as did the laboratory CI data) but instead from 6 to 42. This was because the field data yielded only 6 rating scales which met the apriori cutoffcriteria for inclusion in the CI. Since a range of 1 to 7 was used in rating each scale item, the possible CI range was defined by the products of 6 and 1 at the low end and 6 and 7 at the high end. Even though the text indicates a 7 to 49 scale, the range of 6 to 42 was used in the field comfort data analyses (covered on pages 166-169) which stand correct as published.
Second, Fig. 8 on page 174, along with its related discussion, is inaccurate due to the aforementioned difference in scaling range between the laboratory and field data. A corrected Fig. 8 appears below. So that differences in comfort between the two settings would not be influenced by the differences in rating scales ranges (i.e. CI of 7 to 49 in the laboratory versus 6 to 42 in the field study), the mean CI values (a range from 1 to 7) for each subject's ratings appear in the figure and were statistically analyzed, rather than the linear sum CI ratings as done previously. Of the laboratory observations, those 335