From September 12, 2016, Google Adwords will show null Quality Scores (designated by “--” in the table) if there are not enough impressions or clicks to accurately determine a keyword’s Quality Score.
New keywords will get a null quality score as well. Right now, any new keyword gets a quality score of 6 and a value of average for their ad relevance, landing page experience and CTR.
Null quality scores of “--” will be excluded by default, if the advertiser use reports or automated rules that include a filter on the quality score column.