Spreadsheets are the most popular live programming environments, but they are also notoriously fault-prone.
Hermans & van der Storm (2015)
Never assume a spreadsheet is right, even your own.
Raffensperger (2001)
Spreadsheet development must embrace extensive testing in order to be taken seriously as a profession.
Bock (2016)
Spreadsheet errors... a great, often unrecognised, risk to corporate decision making & financial integrity.
Chadwick (2002)
Most large spreadsheets have dozens or even hundreds of errors.
Panko & Ordway (2005)
The software that end users are creating... is riddled with errors.
Burnett & Myers (2014)
A lot of decisions are being made on the basis of some bad numbers.
Ross (1996)
Spreadsheets are easy to use and very hard to check.
Chen & Chan (2000)
...few incidents of spreadsheet errors are made public and these are usually not revealed by choice.
Kruck & Sheetz (2001)
Spreadsheets are dangerous to their authors and others.
Durusau & Hunting (2015)
It is irrational to expect large error-free spreadsheets.
Panko (2013)
94% of the 88 spreadsheets audited in 7 studies have contained errors.
Panko (2008)
Spreadsheets are extraordinarily and unacceptably prone to error.
Dunn (2010)
Developing an error-free spreadsheet has been a problem since the beginning of end-user computing.
Mireault (2015)
Spreadsheets are often hard, if not impossible, to understand.
Mireault & Gresham (2015)
Most executives do not really check or verify the accuracy or validity of [their] spreadsheets...
Teo & Tan (1999)
Spreadsheets are commonly used and commonly flawed.
Caulkins, Morrison, & Weidemann (2008)
Spreadsheet errors are pervasive, stubborn, ubiquitous and complex.
Irons (2003)
Overconfidence is one of the most substantial causes of spreadsheet errors.
Sakal, et al (2015)
The quality and reliability of spreadsheets is known to be poor.
Bishop & McDaid (2007)
Research on spreadsheet errors is substantial, compelling, and unanimous.
Panko (2015)
Every study that has looked for errors has found them... in considerable abundance.
Panko & Halverson (1996)
Despite being staggeringly error prone, spreadsheets are a highly flexible programming environment.
Abreu, et al (2015)
60% of large companies feel 'Spreadsheet Hell' describes their reliance on spreadsheets.
Murphy (2007)
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)
The untested spreadsheet is as dangerous and untrustworthy as an untested program.
Price (2006)
Programmers exhibit unwarranted confidence in the correctness of their spreadsheets.
Krishna, et al (2001)
1% of all formulas in operational spreadsheets are in error.
Powell, Baker, & Lawson (2009)
Spreadsheet shortcomings can significantly hamper an organization's business operation.
Reschenhofer & Matthes (2015)
Despite overwhelming and unanimous evidence... companies have continued to ignore spreadsheet error risks.
Panko (2014)
Spreadsheets can be viewed as a highly flexible programming environment for end users.
Abreu, et al (2015)
Spreadsheets are alarmingly error-prone to write.
Paine (2001)
Errors in spreadsheets... result in incorrect decisions being made and significant losses incurred.
Beaman, et al (2005)
Spreadsheets are notoriously error-prone.
Cunha, et al (2011)
Even obvious, elementary errors in very simple, clearly documented spreadsheets are... difficult to find.
Galletta, et al (1993)
Spreadsheet errors are still the rule rather than the exception.
Nixon & O'Hara (2010)
Spreadsheet errors have resulted in huge financial losses.
Abraham & Erwig (2007)
Untested spreadsheets are riddled with errors.
Miller (2005)
Errors in spreadsheets are as ubiquitous as spreadsheets themselves.
Colbenz (2005)
Spreadsheets are more fault-prone than other software.
Kulesz & Ostberg (2013)
A significant proportion of spreadsheets have severe quality problems.
Ayalew (2007)
Your spreadsheets may be disasters in the making.
Caulkins, Morrison, & Weidemann (2006)
Spreadsheets contain errors at an alarmingly high rate.
Abraham, et al (2005)
People tend to believe their spreadsheets are more accurate than they really are.
Caulkins, Morrison, & Weidemann (2006)
It is now widely accepted that errors in spreadsheets are both common and potentially dangerous.
Nixon & O'Hara (2010)
The issue is not whether there is an error but how many errors there are and how serious they are.
Panko (2007)
The results given by spreadsheets are often just wrong.
Sajaniemi (1998)
Spreadsheets have a notoriously high number of faults.
Rust, et al (2006)
Studies have shown that there is a high incidence of errors in spreadsheets.
Csernoch & Biro (2013)

Your spreadsheets are wrong

In this article we describe how spreadsheets are riddled with errors, drawing on our own experience and on the research presented in the academic literature on spreadsheet errors and testing.

95% of spreadsheets contain errors

Around 95% of all spreadsheets contain errors. So, unless you've been extremely diligent, or perhaps just very lucky, then it is almost certain that your spreadsheets are wrong. The spreadsheets that you rely on – to inform decision making, do reporting, and generally conduct analysis of just about everything – are probably giving you incorrect results.

How do we know your spreadsheets are wrong?

Budget spreadsheet - is it right?
Budget spreadsheet - is it right?
Can you spot the two errors affecting six cells?

We know your spreadsheets are wrong because we've been there, done that. Our own extensive experience in building, working with, and testing spreadsheets tells us that just about every spreadsheet contains serious flaws.

From hard fought experience we understand what it is like developing and using spreadsheets in the real world – the time pressures, budget limitations, short-cuts, approximations, and everything else that is needed to just get the job done.

Along the way we've made our fair share of mistakes, so we know that awful feeling of going to see the boss to confess that the spreadsheet was wrong.

Every study that has looked for spreadsheet errors has found them

It isn't just our experience that tells us that spreadsheet errors are common. The following quotes from the academic literature on spreadsheet errors are quite sobering:

That last quote is particularly interesting. A 1% error rate may not sound like a significant problem. However, it is the rate per formula, and a typical spreadsheet contains hundreds or thousands of formulae. If your spreadsheet contains just 300 formulae, then a 1% error rate means that there is a 95% probability that the spreadsheet contains at least one error.

Note that the issue isn't that spreadsheets are error prone, as such. Rather, the issue is that humans are error prone. We make errors all the time, but we tend to not notice most of them. This human tendency is well understood in the context of developing other types of computer programs, so programmers do extensive testing of their applications. Spreadsheet developers, conversely, generally do little or no testing of their spreadsheets.

Your spreadsheets need to be tested

Because your spreadsheets almost certainly contain errors, they need to be tested. Beware of being over-confident about your spreadsheets – as Caulkins, Morrison, & Weidemann (2006) observed, "People tend to believe their spreadsheets are more accurate than they really are".

Further information on spreadsheet errors

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