Physiological synchrony refers to the degree to which physiological measures such as heart rate and electrodermal activity (EDA) across multiple individuals uniformly change. Physiological synchrony has shown to be informative of attention among individuals presented with a narrative stimulus: higher physiological synchrony is often related with better attention to the narrative. However, results are strongly dependent on basic factors such as group size and recording length. In the current work we explore what group size and recording length are needed for robust physiological synchrony results