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Model audit

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Title: Model audit  
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Subject: Business economics, Energy development, Financial statement, Spreadsheet
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Model audit

A model audit is the colloquial term for the tasks performed when conducting investors alike that the calculations and assumptions within the model are correct, and that the results produced by the model can be relied upon. When a comprehensive review of the model is required, the scope of review is often extended to include tax and accounting, sensitivity testing and the checking of data contained within the model back to the original financing and legal documentation.


The purpose of a model audit is to provide assurance that the results can be relied upon. For this reason, the party conducting the review will provide a level of reliance on the form of an amount of liability. This may range from a multiple of the fee (2×, 3×, 4× fee, etc.) to a fixed amount, often up to US$20 million. In the event an error or omission is found in the model due to the model auditor's negligence, the organisation relying on the report may choose to sue the model auditor in order to recover any loss.

The objective of the model audit should be to the reduce financial risk that is being taken on by under the transaction to which the financial model relates. As such, it is more important to ensure that the model audit has the proper scope, and is undertaken using a robust methodology, to identify material errors than to negotiate a liability cap if material errors are not identified. The model audit is not, or at least not as a primary purpose, an insurance policy, it is for reducing the financial risk that is being taken on.

Typical scope

For a full-scope model audit, the following elements would usually be included:

  • A review of the model's logic;
  • A review of the model's consistency with financial and contractual documentation;
  • A review of the model's consistency with local GAAP and tax;
  • A sensitivity review.


Model audit has predominately been related to project finance and infrastructure finance, including Public Private Partnership ("PPP") transactions (including PFI in the UK and P3 in the USA).

Model audits are applicable to any financial model that is used to support the taking on of any financial risk, e.g. valuation models, operational models,[2] refinancing models, portfolio model, M&A models etc.

How is it conducted?

Most financial models are produced using Microsoft Excel. The model will routinely contain a number of pages of input data, a sheet of formulas (the 'workings') which drive the model, and the output pages, which are usually in the form of standard financial statements (balance sheet, income statement, cash flow statement, etc.).

Model auditors may undertake a detailed 'bottom-up' review (cell-by-cell checks) of each unique formula, and/or combine a 'top-down' analysis such as the reperformance of calculations based upon the project's documentation ("shadow modelling"),[3] analytical review of trends in key outputs, sensitivity analysis and commercial sense checking.[4][5]

Debate on alternative approaches

As noted in the citations, Andy Hucknall of BDO LLP (and many others) argues that the combination of a detailed 'bottom up' all-cells review with 'top-down' analytical review gives the greatest assurance.

An approach including an 'all cells' review provides assurance on the detailed model logic, as issues related to options not currently active in the Model, such as scenarios or alternative inputs, will not be identified where a reperformance only approach is used as such issues will only be identified by carefully reviewed a model's logic. That said, an 'all cells' review without 'top down' analytical review would lose context, so it is important to use both techniques.

An alternative approach, put forward by Jerome Brice of Mazars LLP, is that a focus on shadow modelling is a superior approach. Implementing, this alternative approach has led to Mazars LLP becoming one of the leading model auditors in global project finance.

Providers of model audit services

Given that the concept of formal financial model audits is thought to have started with early UK PFIs, many of the long-standing financial model audit firms are based in London.

Some of best known model audit firms are:

  • BDO LLP (having merged with PKF (UK) LLP)
  • Corality Financial Group (Sydney and London offices)
  • Deloitte
  • Ernst & Young
  • KPMG
  • Mazars LLP
  • Operis (London and Toronto offices)
  • Protiviti
  • PwC (PwC Australia was joined by the Mercer Model Audit team in 2013)

Some newer entrants to the market are based in Australia but service a global market, such as:

  • Access Analytic (Perth)

Many of the above firms, such as PwC, BDO, E&Y, Mazars and KPMG, are major accounting firms. This enables them to provide the reviews of the tax and accounting in the model, which is usually required in a model audit, either in-house or through their internationals networks. This avoids the need for separate team of the use of subcontractors. It is also likely that the accounting firms will be providing other services to the transaction such as tax advice or financial, commercial and operational due diligence, and the model audit is provided as part of the package. The benefits of using a major accounting firm includes a less complicated engagement process which balances the benefit of using more specialised providers such as Operis, Corality and Protivity.

Software for model audit

Spreadsheet tools and software are useful to the model auditor for assessing the model, providing a work plan and for identifying potential errors, but can not replace a properly planned, scoped and undertaken model audit. Commonly used tools include OAK, SpreadsheetProfessional, SpreadsheetAdvantage, Arixcel Explorer, and The Audinator but there are many others.

Changed environment of the credit crunch

Banks are now more risk averse. Given that they do not pay for the model audit (the sponsors do), but they rely upon the model audit report, they are able to dictate the scope of the model audit. Given that the banks will now insist on a properly scoped model audit, the model audit will finally be seen as a critical financial risk management task, rather than simply have someone to sue if things go wrong.

Competitive dialogue for PPPs

Procurement of public-private projects is often undertaken under a competitive dialogue regime. This requires bidders to commit earlier in the process, and the implication of not identifying errors in a financial model at any early stage could be that a bidder is unable to rectify the error.

As a result, financial models are being checked earlier in the bid process, not just at financial close - these are known as pre-preferred bidder reviews. In some cases, these will have almost the same scope as a financial close model audit (but with documentation review limited as this will still be being drafted), but in other cases, the pre-preferred bidder review will be limited to an agreed scope of procedures with the objective of maximising risk mitigation whilst minimising the fee. The benefits of a pre-preferred bidder review is that it should lead to a reduced model audit fee at financial close.

The introduction of this process to North America has been controversial. The City of Brampton, for instance, has faced lawsuits[6] and controversy[7][8] about use of the process.

Cost and duration

A model audit may take between 1 and 5 weeks, but this does not include the time taken by the model author to rectify the errors identified by the model auditor. The fee is largely dependent upon the scope of review, the number and complexity of the unique formulae in the model, the volume and complexity of the documentation and the number of versions of the model/documentation to be reviewed.

The cost will also depend on the seniority of staff undertaking the work. Planning of the model audit, as for a statutory audit, is vital to mitigating risk, and thus this needs to be undertaken by senior staff. In planning, the elements of the model audit should be allocated to staff with the appropriate level of experience, technical expertise (e.g. tax or accounting) and seniority. The senior staff needs to look at the big picture of the model to ensure that it makes sense as a whole.

See also


  1. ^ Panko, Raymond (1997–2005). "Errors During Spreadsheet Development Experiments". Study.  
  2. ^ Brice, Jerome.PPP Bulletin, November 2008
  3. ^ Brice, Jerome. Explanation of alternative model audit methodologies
  4. ^ Hucknall, Andy. IJOnline, 18 May 2009
  5. ^ Brice, Jerome. IJ Online, July 2009
  6. ^ Grewal, San (13 July 2011). "He built city hall. Now he’s suing it". The Brampton Guardian (Toronto ON). Retrieved 14 July 2011. 
  7. ^ Douglas, Pam (25 March 2010). "City plans under wraps". The Brampton Guardian (Brampton ON). Retrieved 14 July 2011. 
  8. ^ Douglas, Pam (29 March 2011). "Conflict allegations raised at city". The Brampton Guardian (Brampton ON). Retrieved 14 July 2011. 
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