Quality Scores

Q (Quality) scores are defined as a property that is logarithmically related to the base calling error probabilities (P).

Calculating Phred Quality Scores - Base calling accuracy

$$ Q = -10 \log_{10} P $$

Q represents the sequencing quality score of a given base Q

P represents the probability of base call being wrong

Table source: https://www.illumina.com/Documents/products/technotes/technote_Q-Scores.pdf

While next-generation sequencing metrics vary from those of Sanger sequencing (e.g., no electropherogram peak heights), the process of generating a Phred quality scoring scheme is largely the same.