As picked up by the Seroundtable, an AdwordsAPIAdvisor has explained the rough minimum bid ranges that in turn reflect whether your quality score is determined as, ‘Great’, ‘OK’ or ‘Poor’.

On Google groups he explains –

Since a minimum bid is a direct reflection of the Quality Score, the data in this new column (values: Great/Okay/Poor) can help advertisers decide if they should take any action to improve

Just to give you a rough estimate of how minimum bids and thesequality “buckets” currently align… “Great” keywords have a minimumbid less than or equal to $0.04, “Okay” keywords have a minimum bid between $0.05 and $0.30, and “Poor” keywords have a minimum bid thatis higher than $0.30.

The above minimum bid ranges may change over time.