Understanding Psychology (10th Ed)

normal distribution
A distribution of 
scores that produces a symmetrical, 
bell-shaped curve in which the right 
half mirrors the left half and in which 
the mean, median, and mode all have 
the same value.
FIGURE 3 
In a normal distribution, the 
mean, median, and mode are identical, 
thus falling at the center of the 
distribution.
Mean 
Median 
Mode 
FIGURE 4 
In this skewed distribution, 
most scores are low.
Mean 
Median 
Mode 
Low scores 
High scores 
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Module 56 
Descriptive Statistics 
A-9
addition problems, the scores would probably form a distribution in which high scores 
predominated as in Figure 5. Both distributions are skewed although in opposite direc-
tions, and the mean, median, and mode are different from one another. 
FIGURE 5 
In this example of a skewed 
distribution, there tend to be more high 
scores than low scores.
Mean 
Median 
Mode 
Low scores 
High scores 
R E C A P / E V A L U A T E / R E T H I N K
K E Y T E R M S 
R E C A P 
What measures can we use to summarize sets of data?
• Statistics is concerned with collecting, organizing, analyz-
ing, and drawing conclusions from numerical data. (p. A-5)
• Descriptive statistics provides a means of summarizing 
data and presenting it in a usable and convenient form. 
(p. A-5)
• A frequency distribution arranges scores from a sample 
by indicating how often a particular score is presented. 
A histogram, or bar graph, presents the same data 
pictorially. (p. A-5)
• Central tendency is the most representative score in a 
distribution of scores. The mean (or average) is generally 
the best measure of central tendency. The median is the 
point or score in a distribution that divides the distribu-
tion in half so that half the scores are higher and half are 
lower. The third measure of central tendency is the 
mode, the most frequently occurring score in a distribu-
tion of scores. (p. A-6)