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17 Common Spreadsheet Mistakes

My Father used to tell me a knife in the hand of a murderer leads to death but a knife in the hand of a surgeon leads to life. Excel is like that knife. Ok, ok this may be a far stretch (I hope) but in both instances the same tool can lead to different outcomes.

Spreadsheet design is part art and part science. It involves not only technical expertise but also attention to aesthetics. There are two types of errors which can be made when working with spreadsheets: syntax and logical, to borrow nomenclature from the software development world. Syntax errors involve the disobeying of predetermined rules or structures. Those errors are typically picked up by Excel. For example mistyping a formula name or dividing by a zero automatically initiates a red flag.

The second type of errors are a bit harder to pinpoint; those are logical mistakes. These errors are more nuanced; they involve judgments, assumptions or simple oversights. The following is a list of logical errors to watch out for:

1. Cell Reference –Far too often formulas and pivot tables are referencing the wrong range or only a portion of the needed data. That happens when data is moved or added without recalling the dependent formulas.

2. “Elementary my dear Watson, elementary”- Sherlock Holmes stressed to his companion Watson the need to pay attention to the little things…the details. In elementary school we learned the order of operations for mathematical computations. That must be respected. To reiterate, that may seem elementary, but it is quite easy to design formulas that are completely incorrect. Use parentheses to protect and respect that order.

3. Computation Components – That involves performing computations on data which do not agree. For example, attempting to attain total sales by multiplying two quantities rather than unit price and quantity. This will lead to the wrong totals.

4. Hardcoded numbers – At times for one reason or another, formulas may be hardcoded with a value. However, if the document author is still under the impression that a formula is still located there, that can have some unintended consequences

5. Disbursed variables\assumptions – That error is part aesthetic, part function. Centralizing all assumptions and variables aids in the proper digestion of a spreadsheet. Users of the spreadsheet do not have to hunt and peck throughout a workbook to input variables or discern assumptions. Make it simple for them, centralize it on one worksheet. Use space sparingly. A spreadsheet has 65,536 rows and 256 columns in versions older than 2007 and 1,048,576 rows and 16,383 columns for 2007. Just because all of these rows exist doesn’t mean they should be used. Centralize, place charts, summary tables, graphs and input variables in well positioned areas. The only exception to this rule is backup data which can take up as much space as needed. That helps in audits and review if information is centralized and fewer tabs are present.

6. Readability – Simplify important content to be reviewed. Typically Executives and Managers do not have much time to decipher and review Excel spreadsheets. Make it easy for them, summarize relevant data when possible. Point them to the outcomes they are looking to analyze. Users typically focus more on information in the top left corner of a spreadsheet than permeating out. Place the most important information in this area.

7. Hidden Sheets\Column – Hide sheets cautiously. Keep in mind the recipient of the document and its potential path. Sometimes hiding a worksheet is used as a security measure, a mechanism to conceal sensitive information. To put it bluntly, it is not a security measure. Not only can the user unhide those sheets unless protected, printing the entire workbook through the print menu will print those pages as well. A better solution would be to hardcode the dependent variables and remove the sheet before publishing. Special attention is needed when dealing with data related to salary and identification markers like social security numbers. Go the extra mile to protect this information.

8. Lack of formula checks – Make sure there are formula checks for your spreadsheet. For example in accounting all journal entries must equal zero when totaled. Debits must equal credits. At times while manipulating a spreadsheet to reconcile differences the entry may become out of balance where debits no longer equal credits. That can be tracked by implementing a formula which sums the entries on the sheet to ensure that an entry does not fall out of balance.

9. Complex formula – Simplicity still reigns. At times there may be an urge to cram everything into one formula. Resist that urge to create heavily nested lengthy formulas. Use named ranges and break up formulas to add clarity.

10. Comment Sparingly –Whether it is comments within cells to alert users to important information or internal comments within the cell as a reminder to the developer, comment judiciously. I had a Professor years ago who said “If you label everything an emergency, then what you are really saying is nothing is important.” This holds true for comments. Over-commenting can actually send the wrong message to a user. It signals to the user that the comments as a collective do not deserve attention. This would be similar to highlighting an entire book when only a few lines or a paragraph needs attention.

11. Intuitive – It is a kind of an overarching mistake. Always keep the user in mind by asking yourself what is simplest for him\her. Though I dislike breaking things down as gaps and overlaps always seem apparent, ask yourself Who? What? Where? and Why? Who is the document to be delivered to? (could be multiple) What needs to be displayed? Too much information is as much of a detractor as too little information. Where else might that document be delivered to? Many times documents may be forwarded to other parties including Senior Management and Trustees, keep this in mind and build it into your design.

12. Duplication without inspection – Review a worksheet, formulas etc. before copies are made. If an error is apparent within one formula replicating it countless times only adds to your troubles. Having one problem is enough, don't compound it.

13. Label charts or tables properly – Graphs, tables and data can be misunderstood and misinterpreted if labeled incorrectly. I was once told that many people only take a cursory look at graphs and tables in particular and omitting a label can leave the user to self interpretation.

14. Lock Cells with formulas – In many instances it is worthwhile to lock important calculations or data to discourage manipulation, involuntary or otherwise. Even though passwords in Excel can potentially be broken, that roadblock or measure will save you some heartache later.

15. Two pairs of eyes are better than one pair – It is along the lines of that old adage “Two heads are better than one”. Having a spreadsheet reviewed and critiqued by another party can yield a great benefit. It can assist in locating overlooked errors and lead to improved design. Also, the second individual acts as a “sanity check”, verifying that the spreadsheet is delivering its message clearly and error free.

16. Aesthetics – The look and feel of a spreadsheet can add to the clarity of a report or detract from it. A spreadsheet that presents information in an unclear and stale fashion is doomed to be rendered useless. The majority of people would rather look at a graphical representation than a flood of numbers. Use that knowledge and try to roll up important information in a graphical format.

17. Color – That point is along the lines of aesthetics. Colors carry meaning and invoke emotions. I am not suggesting spreadsheet authors take an interior design class or study hue theory, but use this knowledge of colors in your design. This is one of the reasons that negative numbers are represented in red and with brackets in the accounting world. This is to bring attention to the figure.

In short, the message here is to simplify. Many times spreadsheets are designed without the user(s) or end recipient in mind. This is very much like an oral presentation; keep your audience in mind.


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