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Some of the guidelines given for preparing Frequency distribution for grouped data or "Grouped Frequency Distribution" are given below. I have some doubts regarding the same

  1. All classes or groups should have the same interval. So a class should have a range of say 130-139, 140-149 and so on. Or a range of 500-599, 600-699 and so on.
  2. The lower boundary of each class or group should be a multiple of the class or group interval. Taking the same example below, the first set of class is a multiple of 10 (i.e. 130-139, 140-149 and so on) while the second set of class is a multiple of 100 (i.e. 500-599, 600-699)

Regarding these I have the following queries Firstly why should the interval of a class be uniform along the entire class/groups. Will it not be helpfull to have classes which are half of the interval? For example we have a class/group as 130-139, 140-144, 145-149, 150-159 and so on. It is possible that with this varying group we might avoid over representation of a particular class thus avoid the bias that comes from collecting a sample from a large population.

Secondly why is it recommended that the lower boundary of the class be a multiple of the interval? Taking the same example given above, maybe in certain conditions it may make sense to have a class of say 135-144, 145-154, 155-164 and so on.

Anybody who can shed light on this would be appreciated.

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