Part III: Measuring hearing-critical job tasks 143 independent t-test for testing hypothesis 7. Data organization and the statistical analysis were performed using the Statistical Package for Social Sciences version 25.0 (Armonk New York USA). Results Experiment 1 The experiment was completed by all included subjects, and there was no missing data. A normal distribution was confirmed for all SNR50 values. The range varied from 6.9 to 16.5 dbA per driving condition. For theDSDsignals, themeanSNR50 variedbetween–30.2 and–23.4dBAwith ICCs between 0.16 and 0.67 (Table 1). SEMs ranged from 1.2 to 2.0 dBA, corresponding to SDCs between 3.2 and 5.6. For the ATP signal, the mean SNR50 varied widely between –47.3 and –23.6 dBA with ICCs between 0.53 and 0.81. SEMs ranged from 1.3 to 2.7 dBA, corresponding to SDCs between 3.6 and 7.4 dBA. No systematic differences were observed between the first and the second assessment of the signal detection tests. Table 1. Reproducibility of measurement of the signal-detection test for the DSD and ATP signal in the ambient noise of six different train types Mean ± SD in dBA ICC Meandiff SDdiff LoA low ; up SEM SDC DSD signal Mat’64 -23.4 ± 2.1 .66 0.2 1.8 -3.3 ; 3.7 1.3 3.5 Loc1800 -26.1 ± 2.3 .29 -0.6 2.8 -6.1 ; 4.8 2.0 5.5 Sprinter -24.6 ± 2.0 .54 0.6 1.9 -3.1 ; 4.3 1.4 3.7 ICM -27.8 ± 2.2 .16 -0.9 2.9 -6.5 ; 4,8 2.0 5.6 mDDm -30.2 ± 2.3 .62 0.4 2.1 -3.6 ; 4.4 1.5 4.0 V-IRM -26.8 ± 2.0 .67 0.4 1.6 -2.8 ; 3.6 1.2 3.2 ATP signal Mat’64 -47.0 ± 3.8 .75 0.8 2.7 -4.5 ; 6.1 1.9 5.3 Loc1800 -39.9 ± 2.5 .73 0.1 1.9 -3.7 ; 3.8 1.4 3.7 Sprinter -47.3 ± 2.8 .81 0.1 1.8 -3.4 ; 3.7 1.3 3.6 ICM -45.5 ± 3.4 .55 -0.3 3.8 -7.7 ; 7.1 2.7 7.4 mDDm -23.6 ± 2.9 .73 -0.6 2.2 -4.9 ; 3.7 1.6 4.3 V-IRM -44.5 ± 2.2 .53 -0.5 2.6 -5.5 ; 4.5 1.8 5.0 DSD indicates Dead Man’s Switch; ATP, Automatic Train Protection; Mean, pooled mean of the two assessments; Meandiff , mean difference between the two assessments; SDdiff, standard deviation of the mean difference; LoA, limits of agreement, SEM, standard error of measurement; SDC, smallest detectable change.
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