Modern commercial hearing aids are often digital aids and they have been designed with a certain concept of what hearing impairment is, what the needs of the hearing-impaired user are and what feasible technical possibilities are offered by technology. Most hearing aid manufacturers nowadays, test the developed aids on a group of patients or potential users to which they have access. However, these tests are often carried out with bias and test only certain aspects of the hearing aid to which the manufacturer wants to attract the attention. Independent testing therefore, seems to become essential. A number of clinical trials have been done in our two clinics. Clinical trials present us with a great number of problems if we want to assess their use and possible positive contribution to communication in patient groups:

• What kind of signal processing is in the hearing aid?

• How does the signal processing affect "normal" assessment procedures?
• How relevant are real-ear measurements and how should they be performed in terms of spectra and method of analysis?
• What adaptations should we make to "standard" procedures (e.g. signal-in-noise determinations) or do we need new procedures?
• How relevant are our testing procedures for real-life situations?
• How can we avoid the "halo" effect of something more advanced or more expensive?
• Should we rely on subjective scores that can easily be biased, or on more objective scores that may not be very relevant?