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\item Prevalence from population-based national prevalence surveys  \end{itemize}  Historically, incidence has been estimated using results from tuberculin survey results\cite{Styblo1985}, showing the following relationship between the annual risk of infection denoted $\lambda$ and the incidence of smear positive TB denoted $I$. $I^+$.  $I^+ = \frac{\lambda \times 10^5}{2 \times 10} = 50.10^{-5} y^{-1}$