Subjective video quality assessment provides a reliable and useful ground truth for the conception of objective quality metrics. This is a mature field with several standardized methodologies. Laboratories use these methodologies but rarely more than one. Selecting the methodology fitting experimental requirements and constraints is a difficult task. In this paper, two popular video quality assessment methodologies are compared. The authors used them for the quality assessment of HDTV, VGA and QVGA sequences. We show that the relation between both methodologies depends on the resolution. This result conducted to consider the precision of the results depending on the number of observers involved. We indicate how many observers are required to obtain the same precision with both methodologies.