If you read Quality Score metrics programmatically from the AdWords API, please be aware that the values reported by the API, starting from around 11am PT on March 26, 2015, may have been artificially low. Correct values are currently being restored, and should be fully stabilized within 24 hours.
This issue is limited to Quality Score reporting only. Auction time signals of quality, which are the signals actually used within the auction for computing Ad Rank and serving ads, are unaffected.
- Adam Ohren, AdWords API Team