Foreword

The comparison of the effectiveness of NAL-NL1 and DSL[i/o] prescription procedures for children was a very valuable exercise from NAL's perspective, and would, I think, have made the late Denis Byrne proud. Denis was always keen to find out whether things that were supposed to work, actually did work in the way intended. Both the NAL and DSL groups went into the collaborative project with a quiet belief that our respective prescriptions were more suitable for children than the other prescription. We thought the DSL procedure would give too much loudness to be comfortable, and the UWO group thought that the NAL procedure would not produce sufficient audibility. Both groups turned out to be half right and half wrong. We both learnt that neither prescription fully met the needs of all the children to which it was prescribed. Most children needed a prescription more adaptive to various listening environments than the compression implicit in either prescription provided. The results have been instrumental in the subsequent revisions of the NAL and DSL prescriptions, resulting in the two prescriptions becoming more similar to each other than was previously the case.

Although neither prescription was better overall than the other, and although both prescriptions gave good speech intelligibility to the children in both countries, there were none-the-less important differences between the two prescriptions, and many children had preferences for one prescription or the other that were consistent across very different types of test evaluations. The research did not fully get to the bottom of the differences between the procedures; some of the differences in frequency response shape just could not be achieved due to limitations in the hearing aids (which were amongst the most flexible on the market at the time the research was performed). The process of evaluation and refinement must therefore continue.

Apart from the findings themselves, the research collaboration process was also instructive. Although we found we had much in common in the way we undertook research, differences in methods, procedures, analysis processes, biases, and the weight we gave to different findings stimulated us to reflect on how research is performed. I commend to any researcher that they undertake a collaboration with skilled and dedicated researchers from the other side of the world (or the other end of the corridor) whenever they can. Be prepared to learn.