Tutoring math, you get asked about statistics.  The tutor offers an article which might be of interest to stats students.

Calculating standard deviation by hand can be laborious.  Keeping track of what you’ve entered, making sure the brackets have been put in right…most people (including myself) will unlikely enter everything correctly the first time.  In a future post, I’ll show a way to organize the procedure so you do succeed.  Today, though, I have some better news:  maybe you don’t have to.

I’ve never met a scientific calculator without a standard deviation function.  Today, for instance, we have the Sharp EL-520W.  I don’t own any other Sharp calculators, but I imagine this process will be similar for most Sharps worth between $8 and $25.

Example:  Find the standard deviation of the following list:  {-18,16,0,45,100,32,27}

Solution: With the Sharp EL-520W, you need to go into STAT mode to access the statistical functions.

Press MODE. You’ll see a choice of NORMAL or STAT. Press 1 for STAT mode. You arrive at another list of choices: SD, LINE, or QUAD. Press 0 for SD. You should now be back at the calculation screen, with STAT 0 showing at top left.

We are ready to enter our numbers, as follows:

Type in -18, then the DATA key. Note: the key’s main label is M+; however, if you look at the printing below it, you’ll see the DATA label in white.

You’ll know if it’s working: after you press the data key, you should see DATA SET= across the top. Right now, a 1 should appear, since -18 is your first number.

Next, type in 16, then press the DATA key. You should now see DATA SET= with a 2. The 2 means, of course, that 16 is your second number.

Continue: enter each number, then DATA. After keying in 27, then DATA, you should see DATA SET= with 7. Having entered all seven values in the data set, you are ready to find the standard deviation.

Look at the 6 key. The σ_x label appears in green just above it to the right. Because σ_x appears in green, we need to press the green ALPHA key to access the σ_x function.

Press ALPHA 6 =. You should get the result 34.9.

A few points:

1) You will notice that the 5 key has a green s_x label above it to the right. s_x means σ_n-1. If your statistics course prefers σ_n-1, use ALPHA 5instead of ALPHA 6.

2) Before entering a new data set, you should clear the memory, so that no old data affects your new results. Therefore, press 2nd F MODE to “Clear All.”

3) When you’re done with statistical calculations, you might want to return to the mode you were at previously. Most likely, it was normal mode. Press MODE 0 to get back.

In upcoming posts, I’ll outline the standard deviation procedure for other scientific calculators.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.