Mitigating EUC Risk Using Model Validation Principles


The challenge associated with simply gauging the risk associated with “end user computing” applications (EUCs)— let alone managing it—is both alarming and overwhelming. Scanning tools designed to detect EUCs can routinely turn up tens of thousands of potential files, even at not especially large financial institutions. Despite the risks inherent in using EUCs for mission-critical calculations, EUCs are prevalent in nearly any institution due to their ease of use and wide-ranging functionality.

This reality has spurred a growing number of operational risk managers to action. And even though EUCs, by definition, do not rise to the level of models, many of these managers are turning to their model risk departments for assistance. This is sensible in many cases because the skills associated with effectively validating a model translate well to reviewing an EUC for reasonableness and accuracy.  Certain model risk management tools can be tailored and scaled to manage burgeoning EUC inventories without breaking the bank.

Identifying an EUC

One risk of reviewing EUCs using personnel accustomed to validating models is the tendency of model validators to do more than is necessary. Subjecting an EUC to a full battery of effective challenges, conceptual soundness assessments, benchmarking, back-testing, and sensitivity analyses is not an efficient use of resources, nor is it typically necessary. To avoid this level of overkill, reviewers ought to be able to quickly recognize when they are looking an EUC and when they are looking at something else.

Sometimes the simplest definitions work best: an EUC is a spreadsheet.

While neither precise, comprehensive, nor 100 percent accurate, that definition is a reasonable approximation. Not every EUC is a spreadsheet (some are Access databases) but the overwhelming majority of EUCs we see are Excel files. And not every Excel file is an EUC—conference room schedules and other files in Excel that do not do any serious calculating do not pose EUC risk. Some Excel spreadsheets are models, of course, and if an EUC review discovers quantitative estimates in a spreadsheet used to compute forecasts, then analysts should be empowered to flag such applications for review and possible inclusion in the institution’s formal model inventory. Once the dust has settled, however, the final EUC inventory is likely to contain almost exclusively spreadsheets.

Building an EUC Inventory

EUCs are not models, but much of what goes into building a model inventory applies equally well to building an EUC inventory. Because the overwhelming majority of EUCs are Excel files, the search for latent EUCs typically begins with an automated search for files with .xls and .xlsx extensions. Many commercially available tools conduct these sorts of scans. The exercise typically returns an extensive list of files that must be sifted through.

Simple analytical tools, such as Excel’s “Inquire” add-in, are useful for identifying the number and types of unique calculations in a spreadsheet as well as a spreadsheet’s reliance on external data sources. Spreadsheets with no calculations can likely be excluded from further consideration from the EUC inventory. Likewise, spreadsheets with no data connections (i.e., links to or from other spreadsheets) are unlikely to qualify for the EUC inventory because such files do not typically have significant downstream impact. Spreadsheets with many tabs and hundreds of unique calculations are likely to qualify as EUCs (at least—if not as models) regardless of their specific use.

Most spreadsheets fall somewhere between these two extremes. In many cases, questioning the owners/users of identified spreadsheets is necessary to determine its use and help ascertain any potential institutional risks if the spreadsheet does not work as intended. When making inquiries of spreadsheet owners, open-ended questions may not always be as helpful as those designed to elicit a narrow band of responses. Instead of asking, “What is this spreadsheet used for?” A more effective request would be, “What other systems and files is this spreadsheet used to populate?”

Answers to these sorts of questions aid not only in determining whether a spreadsheet qualifies as an EUC but the risk-rating of the EUC as well.

Testing Requirements

For now, regulator interest in seeing that EUCs are adequately monitored and controlled appears to be outpacing any formal guidance on how to go about doing it.

Absent such guidance, many institutions have started approaching EUC testing like a limited-scope model validation. Effective reviews include a documentation review, a tie-out of input data to authorized, verified sources, an examination of formulas and coding, a form of benchmarking, and an overview of spreadsheet governance and controls.

Documentation Review

Not unlike a model, each EUC should be accompanied by documentation that explains its purpose and how it accomplishes what it intends to do. Documentation should describe the source of input data and what the EUC does with it. Sufficient information should be provided for a reasonably informed reviewer to re-create the EUC based solely on the documentation. If a reviewer must guess the purpose of any calculation, then the EUC’s documentation is likely deficient.

Input Review

The reviewer should be able to match input data in the EUC back to an authoritative source. This review can be performed manually; however, any automated lookups used to pull data in from other files should be thoroughly reviewed, as well.

Formula and Function Review

Each formula in the EUC should be independently reviewed to verify that it is consistent with its documented purposes. Reviewers do not need to test the functionality of Excel—e.g., they do not need to test arithmetic functions on a calculator—however, formulas and functions should be reviewed for reasonableness.


A model validation benchmarking exercise generally consists of comparing the subject model’s forecasts with those of a challenger model designed to do the same thing, but perhaps in a different way. Benchmarking an EUC, in contrast, typically involves constructing an independent spreadsheet based on the EUC documentation and making sure it returns the same answers as the EUC.

Governance and Controls

An EUC should ideally be subjected to the same controls requirements as a model. Procedures designed to ensure process checks, access and change control management, output reconciliation, and tolerance levels should be adequately documented.

The extent to which these tools should be applied depends largely on how much risk an EUC poses. Properly classifying EUCs as high-, medium, or low-risk during the inventory process is critical to determining how much effort to invest in the review.

Other model validation elements, such as back-testing, stress testing, and sensitivity analysis, are typically not applicable to an EUC review. Because EUCs are not predictive by definition, these sorts of analyses are not likely to bring much value to an EUC review .


Striking an appropriate balance — leveraging effective model risk management principles without doing more than needs to be done — is the key to ensuring that EUCs are adequately accounted for, well controlled, and functioning properly without incurring unnecessary costs.