Evidence-Based Practice for Nurses

Normal Distributions: Symmetrical Shapes

Measures of central tendencies are used to define distribution patterns. When
the distribution of the data is symmetrical (that is, when the two halves of
the distribution are folded over, they would be superimposed on each other
and therefore be unimodal), then the mean, median, and mode are equal. In
this situation, the data are considered to be normally distributed. A normal
distribution has a distinctive bell-shaped curve and is symmetric about the
mean. In Figure 13-2, note that the decreasing bars, or area under the curve,
indicate that the data cluster at the center and taper away from the mean.

mean and median use continuous-level data values for their calculations, while
the mode can use either continuous- or nominal-data values. The mean is the
most stable in that if repeated samples were drawn from the same population,
the mean would vary less than either the median or the mode would from
sample to sample.

Because it is the most stable, the mean is most often used when computing
other statistics. The median is used when the center of a data set is desired, and
the mode is used to determine the most frequent case.

13.4 Distribution Patterns

1. The most frequent data value in a set of data is the
   a. mean.
   b. median.
   c. mode.
   d. average.


2. When data have no outliers, researchers prefer to report the
   a. mean.
   b. median.
   c. mode.
   d. magnitude.

TEST YOUR KNOWLEDGE 13-3

How did you do? 1. c; 2. a

At the end of this section, you will be able to:

‹ Name patterns of data distribution correctly

KEY TERM

normal

distribution: Data

representation

with a distinctive

bell-shaped curve,

symmetric about

the mean

13.4 Distribution Patterns 341