[Filmed sample size and pragmatic analysis in Down syndrome].

Background: Assessing language development is a complex task that requires practical and theoretical knowledge about the investigated issues. It is also important to take into account data gathering and analysis methodology, in order to achieve consistent and reliable results that mirror the subject's reality.

Aim: considering the purpose of obtaining the maximum data in minimum time, without jeopardizing their quality and effectiveness, our aim is to identify the better sample's size and moment of videotaped interaction to study the pragmatic abilities of children with Down syndrome.