Appendix E 403 



line. This will form the frequency or distribution curve, known 

 also as the "probability curve." It will take the form of a 

 Quetelet curve rising from the lowest class value at the left end 

 of the base-line to an apex at the class of greatest frequency, 

 then dropping to the right end at the highest class value. Such 

 a curve shows at once four things about our data : (1) The 

 extreme values, or the extent of the range, (2) the way in which 

 the individuals are distributed throughout this range, (3) the 

 prevailing type, or class of greatest frequency, and (4) whether 

 the curve is symmetrical, following the normal probability curve 

 or not. If the classes are arranged along the base-line in the 

 sequence of their values instead of their frequencies, the curve 

 will ascend constantly from the lowest value on the left end to- 

 ward the highest value at the right end. This forms a Gallon 

 curve. The Galton type of curve shows merely a different 

 method of exhibiting the frequency distribution of a population 

 that is under study. 



Mode. The class of greatest frequency, the most "popular " 

 or "modish" class, so to speak, is known as the mode or modal 

 class. In our problem, the modal class is 25-34, or the mode is 

 29.5, the mid-value of this class. This is oneway, and an excel- 

 lent one, of expressing type. A typical bean plant of this popu- 

 lation, we can say, is 29.5 cm. long. 



Modal coefficient. It is desirable to know what proportion 

 of the population conforms to this type, or falls into this modal 

 class. This proportion, which is expressed as a percentage des- 

 ignated as the modal coefficient, is found by dividing the number 

 of individuals in the modal class by the total number of indi- 

 viduals measured. In our example, it would be *%% = .3836 = 

 38.36 %, which is the percentage of the population in the class 

 of greatest frequency, hence, the modal coefficient. 



Mean. If one desires to know what an average individual 

 in the population is worth, the mean, symbolized by the letter 

 M, will show it. The mean shows the average value of the 



