RELATION BETWEEN RENTS AND INCOMES 



91 



if not the sole cause of the changes shown in the table above, is the 

 general rise in the le\'el of prices. 



Methods of Study — Graphic Representation. The most convenient 

 and practical method of studying rent distributions is by the use 

 of graphs and charts. The distribution of values of renjs or of other 

 variables may be charted in either a detail or a cumulative form. A 

 detail curve shows at any value of the independent variable the 

 frequency of occurrence of items of that value. A cumulative curve 

 shows at any value of the variable the number (or better, the per 

 cent) of all cases which have values below (or above) that value. 

 Cumulative curves are better than detail curves for presenting rent 

 data since the number of classes into which the data are divided is 

 small and the class widths are non-uniform, resulting in uncertain 



i5 



O 20 



20 30 40 SO 60 70 80 90 100 



Dollars Rent 



10 20 30 40 so eO 70 



Dollars Rent 



Fig. 1 



curves of the detail type.'^ Attempts to compare rent distributions 

 by application of the usual statistical measures of dispersion and 

 skewness have proved unsatisfactory. 



Typical rent distributions plotted in the cumulative manner on 

 ordinary coordinate paper are shown in Fig. 1. Diagrams of this 

 type may be used to determine the rent paid by families of correspond- 

 ing position in the rent scale at the dates of successive surveys, but 

 they do not give a very clear picture of changes in the distribution of 

 rents and from them it is not readily apparent whether rents are 

 closely concentrated or widely distributed in any given case. 



^ Detail curves for rent and income distributions are most easily drawn on paper 

 with a logarithmic scale both ways. 



