That's why you send out a survey to members, asking for their voluntary participation. You ask them what brand they have, the rifle's accuracy, how old it is, sights, etc., which would be defining characteristics, and then you'd ask if the rifle had any failures such as sheared bolts, gas keys that came loose, rust under the FSB, receiver extensions that came loose, etc. What you would get is a general view of the "quality" that makers general produce their rifles with. You would also add in features that the rifle has, as the chart does.
Furthermore, you could include what the survey respondents actually do with the rifle... making it even easier to choose for the average AR buyer.