Microsoft Excel 2010 : Calculating the Mean (part 1) - Understanding Functions, Arguments, and Results

When you’re reading, talking, or thinking about statistics and the word mean comes up, it refers to the total divided by the count. The total of the heights of everyone in your family divided by the number of people in your family. The total price per gallon of gasoline at all the gas stations in your city, divided by the number of gas stations. The total number of a baseball player’s hits divided by the number of at bats.

In the context of statistics, it’s very convenient, and more precise, to use the word mean this way. It avoids the vagueness of the word average, which—as just discussed—can refer to the mean, to the median, or to the mode.

So it’s sort of a shame that Excel uses the function name AVERAGE() instead of MEAN(). Nevertheless, Figure 1 gives an example of how you get a mean using Excel.

Understanding the elements that Excel’s worksheet functions have in common with one another is important to using them properly, and of course you can’t do good statistical analysis in Excel without using the statistical functions properly. There are more statistical worksheet functions in Excel, about one hundred, than any other function category. So I propose to spend some ink here on the elements of worksheet functions in general and statistical functions in particular. A good place to start is with the calculation of the mean, shown in Figure 1.

Understanding Functions, Arguments, and Results

The function that’s depicted in Figure 1, AVERAGE(), is a typical example of statistical worksheet functions.

Defining a Worksheet Function

An Excel worksheet function—more briefly, a function—is just a formula that someone at Microsoft wrote to save you time, effort, and mistakes.

Suppose that Excel had no AVERAGE() function. In that case, to get the result shown in cell B13 of Figure 1, you would have to enter something like this in B13:

=(B2+B3+B4+B5+B6+B7+B8+B9+B10+B11) / 10

Or, if Excel had a SUM() and a COUNT() function but no AVERAGE(), you could use this:

=SUM(B2:B11)/COUNT(B2:B11)

But you don’t need to bother with those because Excel has an AVERAGE() function, and in this case you use it as follows:

=AVERAGE(B2:B11)

So—at least in the cases of Excel’s statistical, mathematical, and financial functions—all the term worksheet function means is a prewritten formula. The function results in a summary value that’s usually based on other, individual values.

Defining Arguments

More terminology: Those “other, individual values” are called arguments. That’s a highfalutin name for the values that you hand off to the function—or, put another way, that you plug into the prewritten formula. In the instance of the function

=AVERAGE(B2:B11)

the range of cells represented by B2:B11 is the function’s argument. The arguments always appear in parentheses following the function.

A single range of cells is regarded as one argument, even though the single range B2:B11 contains ten values. AVERAGE(B2:B11,C2:C11) contains two arguments: one range of ten values in column B and one range of ten values in column C. (Excel has a few functions, such as PI(), which take no arguments but you have to supply the parentheses anyway.)

Many statistical and mathematical functions in Excel take the contents of worksheet cells as their arguments—for example, SUM(A2:A10). Some functions have additional arguments that you use to fine-tune the analysis.

=FREQUENCY(B2:B11,E2:E6)

In this example, suppose that you wanted to categorize the price per gallon data in Figure 1 into five groups: less than $1, between $1 and $2, between $2 and $3 and so on. You could define the limits of those groups by entering the value at the upper limit of the range—that is, $1, $2, $3, $4, and so on—in cells E2:E6. The FREQUENCY() function expects that you will use its first argument to tell it where the individual observations are (here, they’re in B2:B11, called the data array by Excel) and that you’ll use its second argument to tell it where to find the boundaries of the groups (here, E2:E6, called the bins array).

So in the case of the FREQUENCY() function, the arguments have different purposes: The data array argument contains the range address of the values that you want to group, and the bins array argument contains the range address of the boundaries you want to use for the bins.

Contrast that with something such as =SUM(A1, A2, A3), where the SUM() function expects each of its arguments to contribute to the total. To use worksheet functions properly, you must be aware of the purpose of each one of a function’s arguments.

Excel gives you an assist with that. When you start to enter a function into a cell in an Excel worksheet, Excel responds by prompting you for the remaining arguments. See Figure 2, where the user has just begun entering the FREQUENCY() function. Excel displays the names of the arguments in a small pop-up window.

Figure 2. The individual observations are found in the data_array and the bin boundaries are found in the bins_array.

Excel is often finicky about the order in which you supply the arguments. In the prior example, for instance, you get a very different (and very wrong) result if you incorrectly give the bins array address first:

=FREQUENCY(E2:E6,B2:B11)

The order matters if the arguments serve different purposes, as they do in the FREQUENCY() function. If they all serve the same purpose, the order doesn’t matter. For example, =SUM(A2:A10,B2:B10) is equivalent to =SUM(B2:B10,A2:A10) because the only arguments to the SUM() function are its addends.

Defining Return

One final bit of terminology used in functions: When a function calculates its result using the arguments you have supplied, it displays the result in the cell where you entered the function. This process is termed returning the result. For example, the AVERAGE() function returns the mean of the values you supply.