The Essentials of Biostatistics for Physicians, Nurses, and Clinicians

3.3 Frequency Histograms 37

Table 3.3

Frequency and Cumulative Frequency Histogram for BMI Data

Class interval

for BMI levels

Frequency ( f ) Cumulative

frequency ( cf )

Relative

frequency (%)

Cumulative

relative

frequency (%)

18.0 – 20.9 6 6 5.00 5.00
21.0 – 23.9 24 30 20.00 25.00
24.0 – 26.9 32 62 26.67 51.67
27.0 – 29.9 28 90 23.33 75.00
30.0 – 32.9 15 105 12.50 87.50
33.0 – 35.9 9 114 7.50 95.00
36.0 – 38.9 6 120 5.00 100.00
Total 120 120 100.00 100.00

times, and 21.3, 22.7, 23.1, 24.1. 24.3, 24.6, 24.7, 24.8, 25.8, 25.9, 27.5,

28.7, 30.8, 30.9, and 31.6 occur two times. We decide for the histogram

to break the data into 7 equally spaced intervals. The histogram for this

data is displayed here in Table 3.3.

Expressing this as a bar chart, we get Figure 3.1.

Figure 3.1. Relative frequency histogram for BMI data.

Relative Frequency in %

Class Interval

30.00

25.00

20.00

15.00

10.00

5.00

0.00

18.0–20.9 21.0–23.9 24.0–26.9 27.0–29.9 30.0–32.9 33.0–35.9 36.0–38.9