Fig. 3

Relative testing efficiency for various pool-size strategies for CovidNudge sputum PCR testing (3A) across climbing COVID-19 prevalence with (3B) probability of a negative first pool. Legend: 3A. Calculation of the relative efficiency for different pooling strategies as a function of prevalence, where relative efficiency (Er) is defined as \( \mathrm{Er}\kern0.5em =\frac{\mathrm{Number}\kern0.5em \mathrm{test}\mathrm{s}\kern0.5em \mathrm{required}\kern0.5em \mathrm{with}\mathrm{out}\kern0.5em \mathrm{pooling}}{\mathrm{Average}\kern0.5em \mathrm{number}\kern0.5em \mathrm{of}\kern0.5em \mathrm{test}\kern0.5em \mathrm{required}\kern0.5em \mathrm{with}\kern0.5em \mathrm{pooling}\kern0.5em } \) 3B. For prevalence below 2%, pooling of up to 12 samples has a high probability (> 75%) of returning a negative result of first test. As prevalence increases, to maintain high efficiency of pooling, the pool size should decrease. At 5% prevalence, to maintain a 75% probability of a negative first test, the pool size should decrease to 5