Spreadsheets are commonly used and commonly flawed.
Caulkins, Morrison, & Weidemann (2008)
Untested spreadsheets are riddled with errors.
Miller (2005)
Spreadsheets have a notoriously high number of faults.
Rust, et al (2006)
Spreadsheets contain errors at an alarmingly high rate.
Abraham, et al (2005)
The quality and reliability of spreadsheets is known to be poor.
Bishop & McDaid (2007)
Spreadsheet errors... a great, often unrecognised, risk to corporate decision making & financial integrity.
Chadwick (2002)
Spreadsheets are often hard, if not impossible, to understand.
Mireault & Gresham (2015)
A significant proportion of spreadsheets have severe quality problems.
Ayalew (2007)
Spreadsheet shortcomings can significantly hamper an organization's business operation.
Reschenhofer & Matthes (2015)
Spreadsheets are the most popular live programming environments, but they are also notoriously fault-prone.
Hermans & van der Storm (2015)
Every study that has looked for errors has found them... in considerable abundance.
Panko & Halverson (1996)
Most large spreadsheets have dozens or even hundreds of errors.
Panko & Ordway (2005)
Spreadsheets are easy to use and very hard to check.
Chen & Chan (2000)
It is now widely accepted that errors in spreadsheets are both common and potentially dangerous.
Nixon & O'Hara (2010)
Despite being staggeringly error prone, spreadsheets are a highly flexible programming environment.
Abreu, et al (2015)
It is irrational to expect large error-free spreadsheets.
Panko (2013)
Spreadsheets are notoriously error-prone.
Cunha, et al (2011)
Spreadsheets are dangerous to their authors and others.
Durusau & Hunting (2015)
The results given by spreadsheets are often just wrong.
Sajaniemi (1998)
People tend to believe their spreadsheets are more accurate than they really are.
Caulkins, Morrison, & Weidemann (2006)
1% of all formulas in operational spreadsheets are in error.
Powell, Baker, & Lawson (2009)
Studies have shown that there is a high incidence of errors in spreadsheets.
Csernoch & Biro (2013)
Programmers exhibit unwarranted confidence in the correctness of their spreadsheets.
Krishna, et al (2001)
The software that end users are creating... is riddled with errors.
Burnett & Myers (2014)
The untested spreadsheet is as dangerous and untrustworthy as an untested program.
Price (2006)
Overconfidence is one of the most substantial causes of spreadsheet errors.
Sakal, et al (2015)
Errors in spreadsheets are as ubiquitous as spreadsheets themselves.
Colbenz (2005)
Research on spreadsheet errors is substantial, compelling, and unanimous.
Panko (2015)
60% of large companies feel 'Spreadsheet Hell' describes their reliance on spreadsheets.
Murphy (2007)
Errors in spreadsheets... result in incorrect decisions being made and significant losses incurred.
Beaman, et al (2005)
Never assume a spreadsheet is right, even your own.
Raffensperger (2001)
Spreadsheet errors are still the rule rather than the exception.
Nixon & O'Hara (2010)
Spreadsheets are more fault-prone than other software.
Kulesz & Ostberg (2013)
Developing an error-free spreadsheet has been a problem since the beginning of end-user computing.
Mireault (2015)
Despite overwhelming and unanimous evidence... companies have continued to ignore spreadsheet error risks.
Panko (2014)
94% of the 88 spreadsheets audited in 7 studies have contained errors.
Panko (2008)
Spreadsheets are extraordinarily and unacceptably prone to error.
Dunn (2010)
A lot of decisions are being made on the basis of some bad numbers.
Ross (1996)
Spreadsheets can be viewed as a highly flexible programming environment for end users.
Abreu, et al (2015)
Spreadsheets... pose a greater threat to your business than almost anything you can imagine.
Howard (2005)
Every study, without exception, has found error rates much higher than organizations would wish to tolerate.
Panko (1999)
Spreadsheets are alarmingly error-prone to write.
Paine (2001)
Spreadsheet development must embrace extensive testing in order to be taken seriously as a profession.
Bock (2016)
Spreadsheet errors have resulted in huge financial losses.
Abraham & Erwig (2007)
Even obvious, elementary errors in very simple, clearly documented spreadsheets are... difficult to find.
Galletta, et al (1993)
Spreadsheet errors are pervasive, stubborn, ubiquitous and complex.
Irons (2003)
Most executives do not really check or verify the accuracy or validity of [their] spreadsheets...
Teo & Tan (1999)
The issue is not whether there is an error but how many errors there are and how serious they are.
Panko (2007)
Your spreadsheets may be disasters in the making.
Caulkins, Morrison, & Weidemann (2006)
...few incidents of spreadsheet errors are made public and these are usually not revealed by choice.
Kruck & Sheetz (2001)


What is i?

i is a hub for information about spreadsheet best practice, techniques for building better spreadsheets, and testing spreadsheet to find and fix errors.

What does the name i mean?

The name i represents the importance of spreadsheets in decision-making. That is:

  • The "i" represents information, reflecting the role of spreadsheets in decision making.
  • The "n" superscript represents best practice, based on the saying "To the nth degree".

Combining the "i" and the "n" into a mathematical form, i, represents the primary component of spreadsheets — the formulae.

i is pronounced "i-nth" and it is sometimes written that way.

Why are spreadsheets important?

Spreadsheets make a vital, indispensable contribution to decision-making in almost every organisation. The key strengths of spreadsheets are their widespread availability, flexibility, and ease of use.

But these strengths are also a source of risk — since almost anyone in an organisation can develop a spreadsheet, there is often little control over the development process and seldom any testing. The risk of spreadsheet errors is often unrecognised.

For more information, see Making better spreadsheets.

Is there really an academic literature about spreadsheets?

Yes, really.

Many people are surprised that there is an academic literature about spreadsheets. Given the importance of spreadsheets in organisations, and the high incidence of spreadsheet errors, it shouldn't be surprising that spreadsheets have been the subject of formal academic research.

We have collated the academic and practitioner literature about spreadsheets in our Bibliography.

How common are spreadsheet errors?

Virtually every spreadsheet contains errors. The larger and more complex the spreadsheet, the more likely it is to be wrong.

Both academic research and our experience have shown that:

  • Around 95% of spreadsheets contain actual or potential errors.
  • About 1% of all spreadsheet formulae contain an error. This may not sound like much, but even a moderately-sized spreadsheet might contain 1000 formulae, which means that it is likely to have about 10 errors (i.e. 1% of 1000).

Some spreadsheets contain many thousands of formulae, so it is not uncommon for spreadsheets to contain hundreds or even thousands of errors.

For more information, see Calculation cascade: A common cause of catastrophe.

Do I need to test my spreadsheets?

Yes! All spreadsheets need to be tested, otherwise it is likely that your spreadsheets are wrong.

Our approach is to consider the following aspects:

  • Intent. Does the spreadsheet fulfil its intent?
  • Instructions. Are there clear instructions about how to use the spreadsheet?
  • Instruments. Are the instruments (techniques, tools, and algorithms) appropriate?
  • Implementation. Are the instruments implemented correctly?
  • Immunity. To what extent is the spreadsheet immune to errors?

A more detailed description of this methodology can be found at: How to test spreadsheets.

What issues are found when testing spreadsheets?

Even though every spreadsheet is unique, we often see the same types of errors.

Common issues include:

  • "Magic constants" hard coded into a formula.
  • SUM function that omits some cells due to inserting a row or column.
  • Division by zero #DIV/0! errors.
  • Formula that references the wrong cell.
  • Formula that references an empty cell.
  • Formula changed in one cell but not copied to adjacent cells.
  • Incorrect use of absolute and relative references.
  • VLOOKUP or HLOOKUP offset reference is incorrect.
  • VLOOKUP or HLOOKUP assuming that the list is sorted when it isn't.
  • IF statement with an empty [value_if_false] clause.
  • Hidden cells inadvertently included in a calculation.
  • Sub-total included in a total (i.e. double-counting).
  • VBA that has incorrect hard-coded cell references.
  • Incorrect timing of cash flows in an NPV calculation. See Pitfalls of Excel's NPV function.
These are just some common errors — there are many more complex and subtle ways in which spreadsheet errors occur. Have a look at our Blog for more discussion of spreadsheet errors and testing.

What are the consequences of not testing my spreadsheets?

Without rigorous independent testing, your spreadsheets are almost certainly wrong.

There are many examples in the academic literature and in the popular press highlighting the impact of spreadsheets errors. The European Spreadsheet Risks Interest Group (EuSpRIG) has collated a list of spreadsheet horror stories that illustrate common problems and errors that occur with spreadsheets.

Why should I use best practices in my spreadsheets?

It is not just spreadsheet errors that are important. Spreadsheets that are difficult to use, complex to maintain, or poorly documented have significant hidden costs.

In a 2007 survey, 60% of executives agreed that their reliance on spreadsheets could be described as Spreadsheet Hell. Using spreadsheet best practices can help mitigate some of these issues.


Other questions

If you have any other questions, then please contact us.

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