Communication Research
Asking
Questions, Finding Answers
Joann Keyton, Ph.D.
Chapter 10
Descriptive
Statistics
The
Impact of the Standard Deviation on the
A great interactive web site lets you see what happens when the value of a standard deviation changes for a data set. It also lets you see what happens to the normalcy of the data distribution as the number of cases increases. Point your mouse to the black dot at the bottom of the first standards (+1 and –1). When you enter the site, they are set at a standard deviation of 1.25; move the standards closer together to reflect a smaller standard deviation. Notice how this change affects the steepness and slope of the normal curve. Now slide the bin (interval) bar to its lowest value (.05). Click on the button “Create New Histogram.” This feature randomly selects data points and distributes them on the normal curve. Look at the difference between histograms with 100 data points and 500 data points. Using these interactive features you should be see the value of having a greater number of cases in the data set. You should also see how the +1 and –1 standards have a relative position to one another and the mean despite their value.
Mean, Median or Mode?
This website from Virginia Tech provides a good review of measures of central tendency.
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