Interinterpreter variability in determining the SP/AP ratio in clinical electrocochleography.

Calculating the SP/AP ratio in electrocochleography requires the interpreting audiologist to unequivocally identify the peak of the SP wave form. If different points are selected, different SP/AP ratios will result. To investigate this effect, 50 electrocochleographic tracings were sent to 10 different audiologists (500 tracings). Twenty of the wave forms sent to each audiologist were identified as "easy," 10 as "somewhat difficult," 10 as "very difficult," and 10 as "no response." The ranges and standard deviations of the resulting SP/AP ratios were quite high. Analysis of variance showed statistically significant differences in the very difficult and no response group. There is significant interinterpreter difference among SP/AP ratios calculated from the same tracing. This variability affects clinical patient management and investigational projects.