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Scatterplots and Regressions (page 1 of 4) Real life is messy, so it is expected that measurements taken from real life will be messy as well. And when you graph these measurements of real life, it is expected that the dots won't line up exactly in a nice neat line, but will instead form a scattering of dots which, at best, might suggest a nice neat line. These dots are called a scatterplot.
(1, 49),
(3, 51), (4, 52), (6, 52), (6, 53), (7, 53), (8, 54), (11, 56), One of the first things I have to do when graphing these points is figure out what my axis scale values are going to be. If I try doing an axis system with the "standard" –10 to 10 values, none of the above points will even show up on my graph. As is common with these sorts of data sets, all the x- and y-values are positive, so I only really need scales for the first quadrant. The y-values are much larger than the x-values, but instead of squeezing all the y-values together, I'll spread them out (so I can see them better) by using an interrupted scale.
The little "hicky-bob" at the bottom of my y-axis above shows that I've skipped some of the scale values. For some reason, this broken-axis notation is almost never taught in schools, though it is very commonly used in "the real world". If you read financial papers, you're very likely to see many graphs with this sort of axis notation. Don't be surprised if you have to explain this notation to your instructor. You'll probably be expected to do your scatterplots in your graphing calculator. My calculator gives me this picture: Copyright © Elizabeth Stapel 2006-2008 All Rights Reserved
You will often need to adjust your WINDOW settings in order to have all your data points show up on the screen. I used window settings of 0 < X < 25 with an X-scale of 5 and 45 < Y < 65 with a Y-scale of 5 for the above graph. And when you're done with the scatterplot, don't forget to turn the STATPLOT "off", or the parameters for the statistics graphing could mess with your regular graphing utility. I will give you fair warning now: It has become fashionable to insert the topic of scatterplots and regressions into algebra and other non-statistics classes, and to require students to use a graphing calculator to answer questions. While they may give you the slope formula and the Quadratic Formula and all sorts of other stuff on the test (even though you should have memorized them), they will NOT give you help with your calculator. They often don't seem to care if you've learned the math, but you gosh-darned better know your calculator. So pull out your owners manual, or go to the manufacturer's web site, or search online, or get together with a friend NOW, because if you're doing this stuff in class, you ARE going to have to know it, and know it well, on the test. Top | 1 | 2 | 3 | 4 | Return to Index Next >>
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Copyright © 2006-2008 Elizabeth Stapel | About | Terms of Use |
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