Sequencing quality scores measure the probability that a base is called incorrectly. With sequencing by synthesis (SBS) technology, each base in a read is assigned a quality score by a phred-like algorithm1,2, similar to that originally developed for Sanger sequencing experiments.
The sequencing quality score of a given base, Q, is defined by the following equation:
Q = -10log10(e)
where e is the estimated probability of the base call being wrong.
As shown below, a quality score of 20 represents an error rate of 1 in 100, with a corresponding call accuracy of 99%.
Illumina technology enables massively parallel sequencing with optimized SBS chemistry.
Learn MoreQuality Score | Probability of Incorrect Base Call | Inferred Base Call Accuracy |
---|---|---|
10 (Q10) | 1 in 10 | 90% |
20 (Q20) | 1 in 100 | 99% |
30 (Q30) | 1 in 1000 | 99.9% |
Illumina sequencing chemistry delivers high accuracy, with a vast majority of bases scoring Q30 and above. This level of accuracy is ideal for a range of sequencing applications, including clinical research.
Learn how PhiX can be used as an in-run control for run quality monitoring in Illumina NGS.
Read PhiX Technical BulletinFor more in-depth information about sequencing quality scores, read the following technical notes:
Considering bringing NGS to your lab, but unsure where to start? These resources cover key topics in NGS and are designed to help you plan your first experiment.