The Essentials of Biostatistics for Physicians, Nurses, and Clinicians

42 CHAPTER 3 Graphics and Summary Statistics

Figure 3.4. Pie chart for Pugh level for 24 children with liver disease.

12 3 4

567

4%

25%

8%

17% 17%

8%

21%

Bar charts are sometimes used to compare two groups with respect
to a measure. To show the variability in the data that went into the value
presented by the bar, an error bar like the whisker portion of a box plot
is used to show the variability. However, the box plot is a much better
choice for the comparison because it shows the difference between the
medians of the distribution in the proper way and provides more detail
about the variability and skewness of the data.

3.7 MEASURES OF THE CENTER OF

A DISTRIBUTION

There are several measures of central tendency for a data set. They
include

1. arithmetic mean;


2. geometric mean;


3. harmonic mean;


4. mode; and


5. median.