User test: How many users are needed to find the psychophysiological pain points in a journey map?

Abstract

The objective of this research is to investigate how many users are needed in usability testing to identify psychophysiological pain points (PPP) experienced by users during a human-computer interaction (HCI). Fifteen subjects were tested in a new user training context and results show that out of 15 participants, 82% of the total PPP were experienced after 9 participants. Calculations using 1000 trials of random orders were then performed to demonstrate the independence of the order. This research provides guidelines about what could be an ideal sample size for user test using psychophysiological measures.