An erratum
Tell the error Excel warns you about from the one it doesn't: the one that runs without flagging anything and is still wrong.
Free course. Your Maestro, an AI, .
At my first full-time job, as a research assistant at the Public Policy Institute of California (PPIC), we did an analysis of California's community colleges, the state's two-year public colleges. We ran the numbers in Stata, a statistics program, and they were right. To publish them we had to move them to Excel, from Excel to Word, and from Word to a PDF. In one of those passes I inserted some cells in the middle of the table, and from there down everything shifted one cell. The numbers were right, but in the wrong row.
It went past me, the data team, the communications team, and my supervisor, and it was published that way. Afterward we had to publish an erratum.
It happens to everyone. People who study spreadsheet errors, like Raymond Panko, find that on simple tasks people make mistakes at about the same rate, whatever their experience. What made me mad was that nothing warned me at the time. I found out after it was out, when someone else caught it.
Two kinds of error
A formula the AI gives you can fail in two ways.
In the first, Excel warns you. The cell shows #N/A or #NAME?, and you know something needs fixing. It's annoying, but it's the good kind of error: you see it.
The second is like my erratum. The formula has everything it needs and does the math. It does exactly what the formula says, except that isn't always what you wanted. And a formula doesn't show where it gets each value, so if it shows no error, just looking at it won't tell you whether it came out right.
With AI, the second kind matters more. What it gives you almost always looks right: the formula is well written, it runs the first time, and the number that comes out is reasonable. Looking right doesn't tell you whether it counts what you wanted. That's why the question isn't whether it works, but how you know it's right.
What you need to find it
You don't need to know more Excel than the AI. You need to know what should come out. You know how much a café de olla costs at your bakery, what the cash count said, and which products are new this month. The AI doesn't. Over the next three pages you'll use what you already know to find an error of the second kind in the bakery sheet.
Try it
Think about the last time you found an error in a spreadsheet, yours or someone else's. Was it the first kind or the second? What made you suspicious? If it was the second, whatever made you suspicious is exactly what we're going to write down in this course.
Tell your Maestro how you found it.
Check yourself: Which of these is an error of the second kind, the one that doesn't warn you?
Which numbers in your work do you know so well that you'd notice if one came out strange? Write down two or three. You'll use them later.
Reflect: Which numbers in your work do you know so well that you'd notice if one came out strange? Write down two or three. You'll use them later.
Only you and your Maestro read this. It's kept on your account and deleted with it.