What a Youden index of 77 actually means on the OWASP Benchmark

Security tool vendors love a single headline number. The OWASP Benchmark gives one, the Youden index, and it is worth understanding before you compare anything.

What the Youden index is

The OWASP Benchmark runs a tool against about 2,700 test cases, each a known true or false vulnerability, and scores the result as a Youden index from 0 to 100. The index is sensitivity plus specificity minus one, rescaled. In plain terms, it rewards catching real issues and penalizes false alarms at the same time.

Why that matters

A tool can inflate raw precision by quietly reporting fewer findings, or inflate recall by flagging everything. Youden resists both, because dropping true positives hurts sensitivity and flagging noise hurts specificity. So a move from the low 50s to the high 70s is meaningful only if recall held while false positives fell.

How to compare tools fairly

• Ask whether a score is self-measured or verified through the official scoring harness. Both are legitimate, but they are not the same claim.
• Check that the test set and version are stated. The benchmark evolves.
• Separate static-analysis-only numbers from results that include dynamic probing. They measure different things.
• Treat mid-70s and above as the current commercial band, not a finish line.

The point is not any one product. It is that a number only means something when you know how it was measured.