Page:Graphic methods for presenting facts (1914).djvu/184



FREQUENCY CURVES. CORRELATION

Many business problems can be studied most rapidly and conveniently if the data are put in the form of frequency curves. Though engineers have used curves for many years to represent data relating to the laws of physics, the engineer has made practically no use of frequency curves such as are used by the biologist. This is probably due to the fact that the engineer can determine the laws of physics from mathematical computations based on a relatively small number of observations, while the biologist must deal with statistical averages based upon observations and measurements in thousands of different cases. The laws of biology are not so definitely mathematical as those of engineering and physics. The biologist must have more observations than the engineer if he is to draw accurate conclusions.

C. B. Davenport, in Popular Science Monthly

Fig. 140. Frequency Chart Based on the Number of Ribs in Scallop Shells. Shells Are Sorted into Different Piles According to the Number of Ribs, the Piles (from Left to Right) Having Respectively 15, 16, 17, 18, 19 and 20 Ribs

The heights of the different piles show the relative frequency of shells having the different numbers of ribs. Seventeen-rib shells were found much more commonly than shells with any other number of ribs. If a line were drawn through the tops of the different shell piles, we should have a frequency curve

A frequency chart is based on the number of times a certain characteristic is found repeated in a large number of observations. The number of repetitions is referred to as the "frequency". A comparison