**2. Materials and Methods**

#### *2.1. Design*

This study used a within-subjects design and employed a systematic video-coding approach to investigate communicative interaction when children/youths with complex needs used EGAT to interact with their communication partners in natural contexts, comparing this to the NEGAT condition. The study was part of an international multi-center EGAT intervention project, which aimed to examine the effect of a six-month EGAT intervention on participation in activities, communication, and functional independence in everyday life of children and youths with complex needs. Further details of this project can be found in the article by Borgestig et al. [26].

To confront the methodological challenges in a small population target group, a threetiered method proposed for research on AAC use [29] was applied. The strength of this method is to combine group, intermediate and individual analysis to validate group results and provide clinically relevant information [8,29]. The application of three-tiered method for analysis was elaborated in the later Section 2.4.3.
