Yeah, the study authors explicitly say they are low-balling the estimate.

As mentioned earlier, mod logs do not include all moderator activities. For example, replying to moderator mail and deliberation, two types of moderation work reported in prior work (Dosono and Semaan, 2019; Gilbert, 2020) do not appear in mod logs. As a result, our estimate of moderation duration is designed to be a lower bound estimate. Although we provide an underestimate, our work serves as a first step towards quantifying this labor and paves the way for future work to comprehensively quantify moderation hours.

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