Sun March 03, 2013 By:

I am supposed to make a frequency polygon where the classes are 0.5-6.5,6.5-12.5 and so on.the class size is 6 and the first class mark is 3.5.As per the rules i calculated the class mark of the class preceeding 0.5-6.5 which is -2.5. My question is how to plot -2.5 on the histogram, where there is a kink? Moreover, between 3.5 and -2.5 how do we find out the origin?

Expert Reply
Mon March 04, 2013
In a frequency polygon, the class mark/class size is plotted on the x-axis, whereas the frequency is plotted on the y axis. So, in your case, you can easily plot the -2.5 as well as 3.5 mark on the x axis and plot the corresponding frequencies on the y axis and then just join the points to get the frequency polygon. Even if there is a kink, the kink would be on the positive side of the graph. The plotting on a graph does not depend on kink actually, it is just to hide some portion of a graph. To find the origin, just remove kink and plot x axis without it. 
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