Table 3.

Standard deviations of the hearing threshold obtained in test-retest examination (literature data) (separate measurements were carried out for supra-aural headphones (series I, II, III) and in-ear headphones (IV, V, VI) and for the group of young (series I and IV), older (II, V) and the oldest (III, VI) subjects; N=number of subjects) [16-18].

Investigator	Series	N	250	500	1kHz	2kHz	4kHz	8kHz	Mean
Brown 1948 [16]		30	5.3	4.4	5.8	4.5	5.4	7.1	5.4
Erlandsson et al 1979 [17]a		10		6.3	6.2	4.7	5.3	10.4	6.6
Landry et al 1999 [18]	I	20	5.0	4.6	5.2	4.1	4.3	6.0	5.9
	II	10	8.5	7.9	5.2	6.4	9.5	6.9
	III	10	5.9	5.4	6.4	2.1	6.7	7.1
	IV	20	8.8	7.7	4.6	5.5	2.9	3.6
	V	10	7.1	4.4	7.4	5.5	2.6	5.4
	VI	10	9.3	4.6	3.3	5.3	9.0	9.4
Mean			7.1	5.7	5.5	4.8	5.7	7.0	6.0

^aEstimated by comparison with Békésy audiometry performed 5 times on a group of 10 subjects.