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SIMPLE COMPARISONS INVOLVING TIME

United States Statistical Atlas, Census of 1900

Fig. 36. Foreign-born Population of the United States in 1850 Compared with that in 1900, also the Proportion of the Different Nationalities in the Two Years Compared

The method of presentation by means of a circle with sectors is not inaccurate when only component parts are to be shown. Here, however, we have two different circles compared on the basis of total area. The reader cannot compare the areas visually so as to get the correct ratio measure of the increase in total number of foreign-born population. Horizontal bars are much preferable to circles when comparisons are to be made

Though in making comparisons, the horizontal bar divided into blocks is superior to the circle divided into sectors, the circle and sector arrangement is not inaccurate when only the component parts of any unit are to be shown. In the case of Fig. 36, however, the comparison is between two circles, the divisions into component sectors being only an incidental feature. In this diagram, copied direct from the Statistical Atlas of the 1900 Census, it is practically impossible to tell how much larger the foreign-born population was in 1900 than it was in 1850, for it is necessary to compare the two circles on an area basis. To the average person this is an almost impossible task, because it is not feasible to fit one circle inside of the other visually as two horizontal bars may be fitted. If the circle for 1900 were estimated as twice the diameter of the circle for 1850, it would mean that the foreign-born population in 1900 was four times as great as that in 1850. If, however, the ratio were something less simple than this, interpretation of the chart would be difficult even by the processes of mental arithmetic. If the ratio between the diameters were,