It's odd that this is missing. Without it, it's not possible to analyze for biases w.r.t. the stimuli used or even the perceptual features they're adjusting.
There are a few human quality estimate corpuses out there. I know a year or two ago they were re-running the quality assessments with RED camera footage. Check out the NYU/UTexas/Waterloo labs working on SSIM, I bet you can download it.