10 Sensitivity Analysis

Sensitivity analysis is the process by which the robustness of a cost-utility analysis (CUA) is assessed by examining the changes in the results of the analysis when key variables are varied.

In general, uncertainty can be characterised as either parameter-related or modelling-related.

10.1  Parameter Uncertainty

Key Recommendations: Sensitivity analysis should include univariate (simple) analysis and multivariate analysis. When undertaking detailed analysis, probabilistic sensitivity analysis may be necessary. Any uncertainty in the analysis should be fully tested and described in the report.

The following steps should be undertaken to test the level of uncertainty of a parameter (9, 63):

10.1.1   Identify the Parameters

Parameters to consider include those with the greatest level of uncertainty (eg those derived from opinion), and those with the greatest influence on model outcomes (eg key clinical variables and costs).

10.1.2   Specify the Plausible Range over which the parameters may vary

The range over which parameters should be varied in the sensitivity analyses should be based on the available scientific literature, expert opinions, or a scale that is regarded as plausible.

10.1.3   Calculate Results

The level of sensitivity analysis undertaken should be determined by:

  • the impact the results of the analysis could have on the funding decision – if a pharmaceutical is considered to be relatively cost-effective compared with other funding options, but is sensitive to several parameters, more extensive sensitivity analysis should be undertaken than for a pharmaceutical considered likely not to be relatively cost-effective
  • certainty in inputs – if there is significant uncertainty in inputs, for example if surrogate endpoints are used or long-term extrapolation of data is required, more extensive testing needs to be undertaken
  • quality of clinical trials – if the clinical inputs in the analysis were based on trials with a low grade of evidence (eg open-label, high risk of bias, allowed crossover of treatments), more extensive testing should be undertaken
  • risk – further testing is required for high-expenditure pharmaceuticals due to the higher opportunity cost of funding
  • results of sensitivity analysis – if the initial results of a sensitivity analysis indicate some uncertainty in inputs, further testing should be undertaken
  • le