# Characterization and valuation of uncertainty of calibrated parameters in stochastic decision models

## TL;DR

This study investigates how different methods of characterizing uncertainty in calibrated parameters of stochastic decision models affect the valuation of that uncertainty in cost-effectiveness analysis, using a colorectal cancer screening model.

## Contribution

It compares various approaches to uncertainty characterization in a Bayesian calibration framework and assesses their impact on decision-making value of information estimates.

## Key findings

- Ignoring parameter correlation overestimates uncertainty value.
- Full posterior distributions yield similar expected information value as MAP estimates.
- Different uncertainty characterizations significantly influence the estimated value of reducing uncertainty.

## Abstract

We evaluated the implications of different approaches to characterize uncertainty of calibrated parameters of stochastic decision models (DMs) in the quantified value of such uncertainty in decision making. We used a microsimulation DM of colorectal cancer (CRC) screening to conduct a cost-effectiveness analysis (CEA) of a 10-year colonoscopy screening. We calibrated the natural history model of CRC to epidemiological data with different degrees of uncertainty and obtained the joint posterior distribution of the parameters using a Bayesian approach. We conducted a probabilistic sensitivity analysis (PSA) on all the model parameters with different characterizations of uncertainty of the calibrated parameters and estimated the value of uncertainty of the different characterizations with a value of information analysis. All analyses were conducted using high performance computing resources running the Extreme-scale Model Exploration with Swift (EMEWS) framework. The posterior distribution had high correlation among some parameters. The parameters of the Weibull hazard function for the age of onset of adenomas had the highest posterior correlation of -0.958. Considering full posterior distributions and the maximum-a-posteriori estimate of the calibrated parameters, there is little difference on the spread of the distribution of the CEA outcomes with a similar expected value of perfect information (EVPI) of \$653 and \$685, respectively, at a WTP of \$66,000/QALY. Ignoring correlation on the posterior distribution of the calibrated parameters, produced the widest distribution of CEA outcomes and the highest EVPI of \$809 at the same WTP. Different characterizations of uncertainty of calibrated parameters have implications on the expect value of reducing uncertainty on the CEA. Ignoring inherent correlation among calibrated parameters on a PSA overestimates the value of uncertainty.

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Source: https://tomesphere.com/paper/1906.04668