Ok... in the gray world of Google's algorithm, are you finding that the quality score is based on the account or each individual campaign?
quality score is assessed on many different levels account, campaign, adgroup, keyword, text ad and url. Each one has a quality score, but the only transparent quality score is keyword, which can easily be viewed within the keyword tab by unhiding the QS column. QS is mostly attributed to CTR and CTR is mostly dependent on the text ads mapped to the keyword. keyword quality score is equivalent to your min bid. The lower your min bid, the better your QS is. 0.05 min bid is a great QS. 0.04 min bid is even better. but min bid should not be used as a bidding tool. you may have a 0.04 min but may need a $5 max bid to show up on the 1st page of results
At first it's based on their historical numbers for your chosen keywords. Once they have enough data from your particular mixture of keywords, ads and landing pages, they'll give you one. A couple crappy campaigns in one account can drag down the performance of a good one.