In this paper, we study the impact that the level of experience of participants with immersive multimedia has on 360° video quality assessment. An extensive subjective experiment using the modified absolute category rating with hidden reference (M-ACR-HR) method was conducted. The opinion scores obtained from the participants in this experiment along with other sensor data support this study. The statistical analysis is performed in terms of screening participants' distribution of opinion scores for consistency, average rating time, box plots related to mean opinion scores (MOSs) and differential MOS (DMOS). Detailed results for MOS and DMOS are also provided for reference and test sequences covering a wide range of qualities. Major findings include: (1) Screening detects many outliers for participants with no experience, (2) Average rating times show that experts learn the quality assessment task fast, (3) Participants with no experience provide lower opinion scores in average, (4) DMOS may alleviate the bias in quality rating caused by different levels of experience. © 2019 IEEE.