Fact · Speech recognition
The jiwer README says that when the hypothesis is non-empty and the reference is empty, every word or character in the hypothesis counts as an insertion.
Checked against its source on October 17, 2026
In the source's own words
“When the hypothesis is non-empty, every word or character counts as an insertion”
jiwer: Evaluate your speech-to-text system (README), Jitsi open source project, GitHub, jitsi/jiwer, n.d., Section: A note on empty references.
Open the original- What it measures
- The README gives examples: an empty reference against the hypothesis 'peaceful silence' returns a WER of 2, and jiwer reports three insertions for 'now defined behaviour'. Insertions go in the numerator, so a WER with no reference words can only count what the hypothesis adds.
- What it does not show
- This is jiwer's defined behaviour for version 4.0 and later. Other tools may report an empty reference differently, and the README's examples describe the package, not speech in general.