Fig. 2.

Posterior density distributions of the prevalence of mixed infection $\mathbb{P}(\rho \mid S_D)$ when both the growth rates for minority and majority type cells equal 1 and for different values of the expected number of minority cells in sputum E_min. Bearing in mind that the larger the E_min is, the smaller the mean of the distribution is, the values of E_min that we used are 39, 25, 18, 14, 11, 8, 4. We considered n = 500 patients, n_mix = 75 of whom are detected with mixed infection. A naive estimate from the data would indicate a mixed infection prevalence of approximately n_mix/n = 15%, corresponding to ρ = 0.15. However the posterior distribution has mean close to 0.15 only if E_min is large (E_min > 40). The posterior distributions have a much higher mean as E_min decreases.