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#1 2007-07-18 21:20:27

Daniel123
Member
Registered: 2007-05-23
Posts: 663

Histogram (again!)

I'm not too sure where to make the divisions between the classes  this data either... can anyone help please?

Weight (lbs)     class width      Frequency        Frequency Density
  25-29                  4                    2                          0.50
  30-34                  4                    6                          1.50
  35-39                  4                   17                         4.25
  40-44                  4                   24                         6.00
  45-49                  4                   35                         8.75
  50-54                  4                   27                         6.75
  55-59                  4                   19                         4.75
  60-64                  4                   13                         3.25
  65-69                  4                    5                          1.25
  70-74                  4                    2                          0.50

Another quick question, when drawing a histogram, do I use a broken x-axis at the beginning as the data starts at 25? Or do I just start it from 25?

Thanks!

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#2 2007-07-18 22:28:47

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: Histogram (again!)

Whenever you're given a data table where the class boundaries don't match up, I'd say it's safe to act as if the upper boundary was one higher for each class. (Or to be precise, very very slightly less than one)

They're doing it like that because they don't want to put classes of (for example) 25-30 and 30-35, because then there's confusion as to where 30 goes.

The best way of showing classes is by something like 25≤x<30.


Why did the vector cross the road?
It wanted to be normal.

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#3 2007-07-18 22:43:29

Daniel123
Member
Registered: 2007-05-23
Posts: 663

Re: Histogram (again!)

Ok thanks.. I was thinking, as the question says that the weight values are rounded to the nearest pound, could I split the classes at .5 so the first would end at 29.5 and the second would begin at 29.5 etc?

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#4 2007-07-19 00:30:26

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

Re: Histogram (again!)

Ah, well in that case yes, your way is right.
In fact, forget what I said earlier, that's the standard thing to do (unless you're dealing with ages).


Why did the vector cross the road?
It wanted to be normal.

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