Hallucinations in numerals. Most existing mitigation methods do not focus on the hallucination
of numerals. However, the correctness of numerals in generated text, such as date, quantities and
scalars are important for readers [180, 230, 234]. For example, given the source document “The
optimal oxygen saturation (𝑆𝑝𝑂2) in adults with COVID-19 who are receiving supplemental oxygen is
unknown. However, a target 𝑆𝑝𝑂2 of 92% to 96% seems logical, considering that indirect evidence from
patients without COVID-19 suggests that an 𝑆𝑝𝑂2 of <92% or >96% may be harmful. 5”, the summary
“The target oxygen saturation range for patients with COVID-19 is 82–86%.” includes wrong numbers,
which could be fatal. Currently, some works [137, 180, 230] point out that using commonsense
knowledge can help to gain better numeral representation. And Zhao et al. [234] alleviate numeral
hallucinations by re-ranking candidate-generated summaries based on the verification score of
SurveyofHallucinationinNatural Language Generation