**6. Limitations and future lines of research**

The method used for the collection of auditory pathway information as a measurement instrument is widely validated worldwide.

Among possible random errors, we must take into account the variability of the measurements. We cannot control the child's head movements, even when asleep, by varying the exact distance to the loudspeaker. To minimize sampling variability, we assess the effect of chance by conducting hypothesis test.

To avoid selection bias errors, patients with perfect normal conditions with insertion earphones were selected in order to know which children without pathology could be tested with free-field stimulus.

When comparing tests performed with insert earphones and in the free field, an information bias may occur during the measurement. To avoid this bias as much as possible, we have performed the tests with the same explorer, in the same environmental conditions, with the same equipment, the same data collection, and the same processing.

Finally, there is no confounding bias as we do not want to know a cause-effect relationship in our research.

Future research should be directed toward its application in daily clinical practice with hearing-impaired children, assessing that the responses obtained with free-field stimuli are similar to the ABR/ASSR-MF values in cases of hearing pathology.

We consider the need for free-field stimulus studies in the fitting and follow-up of assistive listening devices, both conventional hearing aids and implantable devices.
