... that you might have heard around 5:50 PM Atlantic Daylight Time was the exact moment the Stats course doffed its sheep's clothing and bared its glistening, red-dripping fangs.
Day Two, and I'm hyperventilating already.
I do okay with formulas as long as I know what each individual component means. But if I don't know what one thing means, then a fire door drops down in my brain, the RED ALERT goes off, and suddenly I'm no longer thinking clearly and nothing is sinking in. Absolutely nothing. I'm pretty sure that when I die and my body is donated to science, it will be a documented fact that my numeracy wiring is a bit awry.
We were going to compute the mean. I know what the mean is, and how to get it. I do know, that is, until you give me this to do it with:
Now, I'm not totally lost. I know that the big funky E-thing is a capital sigma, and it means "sum". And I know what x-bar is, and I know that the n on the bottom is the number of pieces of data that you are dividing by. Where I'm totally confused is the n on top of the sigma, and the i=1 below it, and the x-subscript-i business beside it. And what on earth do all of those positions mean?
HELP?!
Wednesday, May 07, 2008
The bloodcurdling scream ...
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1 comment:
Okay, if you have n values that you're trying to average, you can label each one with a number. So say you're trying to average 5, 7, and 9. You want to label them as your first, second, and third values. One way to do that is to call them x_1, x_2, and x_3 (assume those are subscripted numbers). So x_1 = 5, x_2 = 7, and x_3 = 9.
Now, getting back to the sigma. The stuff on the bottom and top is helping to tell you what you want to add up. You want to add up all n of the values, right? So that's the values numbered 1 through n? That's all the stuff below and above the sigma says. You're going to add up the thing on the right over and over, substituting each possible value in for i. The i=1 means you start by substituting 1 in for i (meaning you start adding with x_1), and then you keep increasing i by 1 until you get to the top number. Since the top number is n, you're going to add up everything up to x_n. In my example, n=3, so you're going to keep going up to x_3. In other words, the sum will be x_1 + x_2 + x_3. In my example, that's 5 + 7 + 9, or 21.
Then the formula shows that you divide that by n to get the mean. In the example, n=3, so you divide 21 by 3 and get 7: that's your mean.
I'm home today - call if this doesn't make enough sense.
Geekiest blog comment ever.
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