“…Several observation schemes exist related to (interactive) play regarding social interaction and physical activity, such as the POS [222], the OPOS [17], MIPO focusing on social functioning [75], the Social Play Continuum 1 , OSMOS focusing on motor skills [50], and often such schemes are adapted and then applied for interactive play evaluation purposes [104,127,157,219,246]. One often used measure for inter-observer reliability is Cohen's κ.…”