1. Each dot represents one carload of cement. Dots in the area marked "one price system" represent sales at prices yielding to the mill its "then current maximum mill net price."

2. Dots in successive outer zones represent sales yielding less than the mill's maximum

mill net by an amount within the range of cents indicated within each zone on the chart. The guide for cents per zone is shown in the South Dakota section.

Chapter 39 CORRELATION CHARTS

THE purpose of correlation charts is to indicate the degree and type of relationship between variables. One form of correlation chart, the scatter diagram, also called the gun-shot or shot-gun chart and buck-shot chart, sometimes indicates that there is no relationship between two variables. See the chart below.

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Dun't Review, August 1938. SCALE .7

The Increase or Decrease of Sales for the Period 1935-37 for Individual Retail Stores in the United States According to Sales Volunne in 1935.

1.

According to the comments in Dun's Review, the wide scatter of individual cases indicates a "growth tendency in favor of small concerns" rather than indicating that "all large stores had built sales volume more rapidly than the small ones."

It should be noted that the vertical rulings are logarithmic.

The limited number of vertical and horizontal rulings was intentional -that is, they were limited to make it easy for the reader to notice the lack of pattern of the dots.