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\item {Results from national TB prevalence surveys.} Incidence is estimated using prevalence survey results combined with either a dynamic model or estimates of the duration of disease. This method is used for 19 countries that accounted for 46\% of the estimated global number of incident cases in 2014.  Incidence can be estimated using measurements from national surveys of the prevalence of TB disease combined with estimates of the duration of disease. Incidence is estimated as the prevalence of TB divided by the average duration of disease.   In practice, the duration of disease cannot be directly measured. For example, measurements of the duration of symptoms in prevalent TB cases that are detected during a prevalence survey are systematically biased towards lower values, since active case-finding truncates the natural history of undiagnosed disease. Measurements of the duration of disease in notified cases ignore the duration of disease among non-notified and untreated cases.   Literature reviews commissioned by the WHO Global Task Force on TB Impact Measurement have provided estimates of the duration of disease in untreated TB cases from the pre-chemotherapy era (before the 1950s). The best estimate of the mean duration of disease (for smear-positive cases and smear-negative cases combined) in HIV-negative individuals is about three years. However, the proportion of incident cases that remain untreated is unknown. There are few data on the duration of disease in HIV-positive individuals.   The assumed distributions of disease durations are shown in Table.  \begin{table}   \begin{tabular}{ c c }  Case category & Distribution of disease duration (year) \\   Notified, HIV-negative & Uniform $(0.2 - 2)$ \\   Not notified, HIV-negative & Uniform $(1 - 4)$ \\   Notified, HIV-positive & Uniform $(0.01 - 1)$ \\   Not notified, HIV-positive & Uniform $(0.01 - 0.2)$ \\   \end{tabular}   \caption{Distribution of disease duration by case category}   \end{table}  \item {Notifications in high-income countries adjusted by a standard factor to account for under-reporting and under-diagnosis.} This method is used for 73 countries (all high-income countries except the Netherlands and the United Kingdom), which accounted for 3\% of the estimated global number of incident cases in 2014.  In the absence of country-specific data on the quality and coverage of TB surveillance systems, it was assumed that TB surveillance systems from countries in the high-income group performed similarly well, although the model does allow for stochastic fluctuations. The exceptions were the United Kingdom and the Netherlands, where the underreporting of TB cases has been measured using inventory studies and capture–recapture modelling\cite{Anderson2010}\cite{17156496}. For these two countries, the results from these studies were used to measure TB incidence directly. 
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