Part III: Measuring hearing-critical job tasks 145 associations were observed between the SNR50 and the subjective rating of locomotive engineers of the effort and concentration it takes to detect auditory warning signals (hypothesis 5). The mean SNR50 was significantly higher (poorer) when the test was performed in the Mat64 compared with the V-IRM (hypothesis 6). The mean SNR50 was significantly higher in hearing aid users compared with non-hearing aid users (hypothesis 7). Therefore, six of the seven hypotheses were confirmed by the results in the test population. Table 3. The construct validity (hypotheses testing) of the signal detection test Hypothesis Confirmed DSD signal ATP signal Yes/no Mat64 VIRM Mat64 VIRM 1.The SNR50 derived with the DSD-signal detection test was expected to show a moderate, positive correlation with the BHI of the pure-tone thresholds at 2000 and 4000Hz. Yes r= .410 r=.523 - - 2.The SNR50 derived with the ATP-signal detection test was expected to show a moderate, positive correlation with the BHI of the pure-tone thresholds at 4000 and 8000Hz. Yes - - r=.744 r=.547 3. The SNR50 derived with the signal detection test was expected to show a moderate, positive correlation with the SNR derived with a speech-in-noise test performed in continuous noise. No r= .143 r= .281 r= .279 r= .312 4. The SNR50 derived with the signal detection test was expected to show a moderate, positive correlation with the SNR derived with a speech-in-noise test performed in fluctuating noise. Yes r= .343 r= .307 r= .337 r=.338 5. The SNR50 derived with the signal detection test was expected to show a moderate, positive correlation with locomotive engineer’s subjective rating of the effort and concentration it takes to detect auditory warning signals at their workplace Yes r=.358 r= .461 r= .364 r=.429 6.The mean SNR50 was expected to be significantly higher when performed in the ambient noise of theMat64 than when performed in the ambient noise of the VIRM. Yes p <.001 p <.001 7. Locomotive engineers who wear hearing aids were expected to score significantly poorer on the signal detection test than locomotive engineers who do not wear hearing aids Yes p <.001 p <.001 p =.010 p =.010 SNR50 indicates Signal-to-Noise Ratio at which 50 percent of the warning signals can be heard, Low, correlation < 0.30; moderate, correlation 0.30-0.70; high, correlation > 0.70.
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