Microsoft Excel Graphs, the Dummies Version

linear fit line in Excel, with equation

As our staffers wander the internet in search of greedy freelancers to pillory, it's fairly common to come across "how-to" posts that misinterpret the question and end up giving the wrong answer. Today's (returning) DotD nominee, eHowian Amy Dombrower, did just that. Oh, sure, she provided a method that works, but we're almost certain she didn't understand the question in "How to Graph Linear Equations in Excel 2007."¹

Dombrower managed to find some excruciatingly detailed instructions somewhere that would actually allow you to plot a graph of a linear equation, and reworded them so that they might have worked if she had understood the mathematical principles of linear equations in the first place. It's a pretty safe bet this J-school grad didn't study much math, though, given her initial definition:

"A linear equation is a formula that expresses a series of values of one axis (y) in terms of the other axis (x)."

Strange, because everyone here thinks that a linear equation expresses one variable in terms of a second variable, but what do we know? We're mostly fact-seeking scientists instead of omniscient journalists. Be that as it may, Amy wants her readers to populate one column of numbers, then use an arcane Excel function to define it as X. Why that's necessary for a two-column spreadsheet is beyond our ken... Then, the "student" is supposed to define the second column thusly: "Enter a linear equation in cell B2. The equation will appear in the Formula Bar. With the format y=mx + b, type '=m*x + b.' When you go to a new cell, Excel will calculate the result of the formula, which will now appear in the cell..."

...yeah, right: "type '=m*x + b'": like that's gonna work, since Amy didn't bother to define either m or b, probably because she had no idea what the variables m and b represent. For those of you keeping track, m is the slope of the linear equation and b is the y-intercept. But Dombrower (and eHow'.coms content editor) apparently didn't know that, so she didn't say what she should have said: "enter a linear equation in the form y = mx + b." Dumbass.

The stupid part is that it's a lot more likely that the OQ wanted to know how to fit a line to an existing scatter plot representing a linear equation. That's an entirely different kettle of fish, but it's easy enough. Create your scatter plot and -- exactly how depends on your version of Excel -- add a trend line. Format the trend line to be a linear fit, and voila! But Dombrower, apparently hoping to be the Dumbass of the Day again, never said so...

¹ The original has been deleted by Leaf Group, but can still be accessed using the Wayback machine at archive.org. Its URL was    ehow.com/how_6312129_graph-linear-equations-excel-2007.html

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