Starting the week of September 12, new keywords and keywords that haven’t received any recent clicks and impressions will be given a reported Quality Score in AdWords of null, represented by dashes (“-“).
Any keywords by default with null Quality Scores will be excluded from reports and automated rules that have Quality Score unless you check a new box that appears with this change to include them. It’s recommended by Google that users should review any reports, filters, rules and scripts that include Quality Score before September 12 to make sure that they will continue performing properly.
This particular change is an update from July 2015, where Google chose to assign new keywords a default reported Quality Score of 6. By assigning a single default Quality Score for new keywords, Google hoped it would “simplify some of our core systems.” The default Quality Score will update once new keywords receive sufficient impressions data.
Originally before the shift, Google used to assign a new keyword a Quality Score that was calculated based on the performance of the keywords across the entire system and the individual account’s historical performance.
Just as an FYI for users, the switch from a default reported score of 6 to null isn’t going to affect the ad auction or the way ads are served. Null is simply a clearer placeholder for reported Quality Score tan a default of 6.