Psy 231 GW04 Variability – study guide
1 What is the overall purpose of measuring variability?
2 Explain what two purposes are served by a good measure of variability.
3 Name and define the four basic measures of variability.
4 Why is the standard deviation the most widely used descriptive measure of variability?
5 What is a “deviation score?”
6 Identify and explain the two parts to a deviation score.
7 When we compute the average, or mean, deviation score, what value always results?
What causes this value to occur?
How do we prevent its occurring when computing standard deviation?
[NOTE: for the purposes of this course, we will focus exclusively on “definitional formulas,” not on
computational formulas, for various statistics.]
8 Using appropriate symbols, write the definitional formula for the sample standard deviation.
Note: write the full definitional formula!
9 Why is n-1 used in the denominator of the formula for the sample standard deviation?
10 Explain “degrees of freedom.”
Specifically, why are only n-l scores free to vary when computing the sample variance?
11 Explain what we mean by an “unbiased” versus a “biased” estimator of a parameter.
13 Briefly explain what standard deviation is and why it is important in descriptive statistics.
14 Sketch a polygon for a sample with M = 24 and SD = 3.
15 Explain the relation between extreme scores and the mean, var & sd.
16 Explain the relation between sample size and the mean, var & sd.
17 Explain “stability under sampling” & its relation to the mean, var & sd.
18 Briefly summarize the reasons that sd is the preferred measure of variability in descriptive statistics.