Phred Quality Scores

From Wikipedia: http://en.wikipedia.org/wiki/Phred_quality_score

Phred Score Translation

Phred quality scores are logarithmically linked to error probabilities

Phred Quality Score	Probability of incorrect base call	Base call accuracy
10	1 in 10	90 %
20	1 in 100	99 %
30	1 in 1000	99.9 %
40	1 in 10000	99.99 %
50	1 in 100000	99.999 %