Page 131 - Statistics for Dummies

Time between Eruptions of Old Faithful (n = 222)
80
60
40
Figure 7-6:
20
Histogram
#3 of Old
Faithful
geyser Number of between-eruption times per group 100 0 Chapter 7: Going by the Numbers: Graphing Numerical Data 115
99
45
90
81
72
63
54
eruption
times. Time between eruptions (minutes)

Examining Boxplots
A boxplot is a one-dimensional graph of numerical data based on the five-
number summary, which includes the minimum value, the 25th percentile
(known as Q ), the median, the 75th percentile (Q ), and the maximum value.
1 3
In essence, these five descriptive statistics divide the data set into four parts;
each part contains 25% of the data. (See Chapter 5 for a full discussion of the
five-number summary.)
Making a boxplot
To make a boxplot, follow these steps:
1. Find the five-number summary of your data set. (Use the steps out-
lined in Chapter 5.)
2. Create a vertical (or horizontal) number line whose scale includes the
numbers in the five-number summary and uses appropriate units of
equal distance from each other.

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