Bayesian history matching of complex infectious disease models using emulation: a tutorial and a case study on HIV in Uganda.
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History matching is an iterative procedure that reduces the simulator's input space by identifying and discarding areas that are unlikely to provide a good match to the empirical data.Simulator evaluations made within this region were found to have a 65% probability of fitting all 18 outputs.Further research is required to explicitly address the stochastic nature of the simulator as well as to account for correlations between outputs.
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PubMed Central - PubMed
Affiliation: Dept. of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, United Kingdom.
ABSTRACT
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Advances in scientific computing have allowed the development of complex models that are being routinely applied to problems in disease epidemiology, public health and decision making. The utility of these models depends in part on how well they can reproduce empirical data. However, fitting such models to real world data is greatly hindered both by large numbers of input and output parameters, and by long run times, such that many modelling studies lack a formal calibration methodology. We present a novel method that has the potential to improve the calibration of complex infectious disease models (hereafter called simulators). We present this in the form of a tutorial and a case study where we history match a dynamic, event-driven, individual-based stochastic HIV simulator, using extensive demographic, behavioural and epidemiological data available from Uganda. The tutorial describes history matching and emulation. History matching is an iterative procedure that reduces the simulator's input space by identifying and discarding areas that are unlikely to provide a good match to the empirical data. History matching relies on the computational efficiency of a Bayesian representation of the simulator, known as an emulator. Emulators mimic the simulator's behaviour, but are often several orders of magnitude faster to evaluate. In the case study, we use a 22 input simulator, fitting its 18 outputs simultaneously. After 9 iterations of history matching, a non-implausible region of the simulator input space was identified that was 10(11) times smaller than the original input space. Simulator evaluations made within this region were found to have a 65% probability of fitting all 18 outputs. History matching and emulation are useful additions to the toolbox of infectious disease modellers. Further research is required to explicitly address the stochastic nature of the simulator as well as to account for correlations between outputs. Related in: MedlinePlus |
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Mentions: Visualising the distribution of the non-implausible points is conveniently done via minimum implausibility and optical depth plots [35], such as the ones shown in Fig. 5. To construct the minimum implausibility points, two inputs are first selected and a rectangular grid covering their range is formed. The non-implausible points are placed in the respective bin of this grid, according to the value of their element. The plot shows the minimum implausibility value among all points in a given bin. Assuming a sufficiently large number of non-implausible samples, this kind of plot provides an empirical estimate of the minimum implausibility that can be expected if we were to fix inputs to a particular value, and hence shows locations in space that can be ruled out as implausible, irrespective of the choices of all the 20 other inputs. The optical depth plots are constructed in the same fashion, but instead of displaying the minimum implausibility per grid point, they display an empirical estimate of the probability of encountering a non-implausible point for a given set of values for inputs . This estimate can be obtained from the ratio of non-implausible to total drawn points per bin. They therefore provide an estimate of the (higher-dimensional) depth of the non-implausible region, conditioned on the inputs . |
View Article: PubMed Central - PubMed
Affiliation: Dept. of Infectious Disease Epidemiology, London School of Hygiene & Tropical Medicine, London, United Kingdom.