Basic Statistics

GRAPHS 43

Table 4.6 Frequency Table of Ages of 302 Deaths from Scarlet Fevera

Age (years) Number of Deaths Relative Frequency

0-

1-

2-

3-

4-

5-

1-

8-

9-

10-

15-20

Sum

18

43

50

60

36

22

21

6

5

14

3

302

.06

.14

.11

.20

.12

.07

.06

.02

.02

.05

.01

1 .oo

a Data are extracted with permission from A. Bradford Hill, Principles of Medical Statistics, Oxford

University Press, New York, 1961, p. 52.

Figure 4.2 Age of 302 deaths from scarlet fever: a histogram.

units high is plotted above the entire class interval. The area of this bar is now 14
square units, as it should be. Frequencies have been plotted in Figure 4.2.

4.2.3 Areas Under the Histogram

As mentioned earlier, the eye tends to compare the areas in a graph rather than the
heights. In interpreting the histogram in Figure 4.l(a), for low-altitude workers, we
might notice that the first, second, and third bars on the left side of the histogram