Negative-to-negative test concordance in school survey.

Note: Fractions represent the number of negative results for each test (numerator) out of those that were negative by the index test (denominator). The results are of the form: proportion (%). The number of negative index tests (denominator) changes by column because it only includes specimens with valid results by the comparison test (numerator).注：此处的分数代表每项检测的阴性结果数（分子），其统计范围限定于经指标检测（index test）判定为阴性的总样本（分母）。结果以「占比（%）」的形式呈现。作为分母的指标检测阴性样本数会随列发生变化，原因在于该分母仅包含经对比检测（comparison test）获得有效结果的样本。