# FAQ

### What is iⁿ?

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 iⁿ 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.

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.

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.

### How common are spreadsheet errors?

Virtually every spreadsheet contains errors. Large and complex spreadsheets are likely to contain many errors.

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.

### Do I need to test my spreadsheets?

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 detailed description is at: i spreadsheet methodology.

### 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 and individual values both 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.