Objectives: One-way sensitivity analyses (OWSA) for cost-effectiveness models are often summarized in the form of a tornado diagrams that offer an easily interpreted method of displaying the impact of changes to input parameters on model results. However, when these changes produce incremental cost-effectiveness ratios (ICERs) in cost-effectiveness quadrants different from the base-case ICER, the basic tornado methodology does not automatically detect the change in quadrants as a sensitive parameter and does not offer ways to show this paradigm in a straightforward manner. Open-source code was developed in two commonly used packages, namely Microsoft Excel using Visual Basic for Applications (VBA) and R, so that end users can easily produce tornado diagrams in all OWSA situations.

Methods: Sets of hypothetical one-way sensitivity analysis results were created for possible OWSA scenarios where ICERs: 1) remain in the same quadrant; 2) fall in two quadrants with different signs (positive/negative); 3) fall in two quadrants with the same sign; and 4) fall in more than two quadrants. Code was written in both packages, quality checked, and tested across multiple development environments.

Results: The resulting open-source code allows the end user to define base-case results and an Excel cell range (VBA) or a data frame (R) that correspond to results of the OWSA. From the results, a tornado diagram is produced that ranks parameters that fall in multiple cost-effectiveness quadrants as the most sensitive and displays results in all quadrants. Tornado diagrams from the four scenarios described above are displayed as well as a graphical view of the process algorithm. Open-source code is available for download and use with attribution.

Conclusions: A transparent and user-friendly algorithm was developed to aid in the production of high-quality tornado diagrams in commonly used modeling software packages. The resulting code is beneficial to both new and experienced model programmers.