k-anonymity
A privacy floor: a cohort figure shows only when at least 10 sites contribute, so no one site can be singled out.
k-anonymity is the rule that keeps benchmarks from leaking any one site's data. A cohort statistic is only displayed when at least 10 (k >= 10) sites contribute to it. Below that, one member could be reverse-engineered from the aggregate, so we suppress the figure and show a forming state.
One caveat we state plainly: k >= 10 guarantees anonymity, not precision. Ten sites make a number safe to show; they do not make it statistically tight. Precision is a separate question, answered by the confidence interval on the figure.