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Nine impressions, though, is surely too low for Google's system to make any sort of judgement about the CTR. They won't disable a word with only 9 (or 90) impressions.
no hard rule matching CTR to "strong" or "moderate" or "at risk"
The keywords strengths are directly related to the CTR on Google's site. It doesn't take into account CTR on the various other properties Adwords are displayed, AOL, Ask, etc. The Google-only CTR is also what determines if your ads get slowed or not, so it's best not to have any at risk.