Re: Number of classes.

[Jon Cryer]

I asked Minitab support how they did it. Here is their answer:

Date: Fri, 26 Sep 1997 15:07:50 -0400
To: [EMAIL PROTECTED]
From: Tech Support 
Subject: number of bars in MINITAB histogram

Jonathan,

I finally found an answer for you.  Here's the algorithm.

There are upper and lower bounds on the number of bars.

Lower bound = Round( (16.0*N)**(1.0/3.0) + 0.5 )
Upper bound = Lower bound + Round(0.5*N)

After you find the bounds, MINITAB will always try to get as close to the
lower bound as it can.

Then we have a "nice numbers" algorithm that finds interval midpoints,
given the constraints on the number of intervals.

But there is special code for date/time data and for highly granular data
(e.g., all 1's and 2's).

Find the largest integer p such that each data value can be written (within
fuzz) as an integer times 10**p.

Let BinWidth = 10**p.

Let BinCount =  1 + Round( ( range of data ) / BinWidth )

If BinCount  is = 10, then let the bin midpoints run from the data min to
the data max in increments of BinWidth.

Otherwise, use the "nice numbers" algorithm.

Hope this helps.

Andy Haines
Minitab, Inc.

At 11:01 PM 1/4/01 -0500, you wrote:
To determine the number of classes for a histogram, Excel uses square root
of the number of observations. Is it also true for the number of
observations greater than 200, say, for 2000?. Does the MINITAB use the same
for determining the number of classes for a histogram?
Any help would be appreciated.





=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=


 ___
--- |   \
Jon Cryer, Professor [EMAIL PROTECTED]   ( )
Dept. of Statistics  www.stat.uiowa.edu/~jcryer \\_University
 and Actuarial Science   office 319-335-0819 \ *   \of Iowa
The University of Iowa   dept.  319-335-0706  \/Hawkeyes
Iowa City, IA 52242  FAX319-335-3017   |__ )
---   V

"It ain't so much the things we don't know that get us into trouble. 
It's the things we do know that just ain't so." --Artemus Ward 


=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

Re: Number of classes.

[dennis roberts]

i randomly generated some data for n=200 and n=2000 from an integer
distribution ranging from 20 to 50 ... in the older graphics mode, here
is what i got


Histogram of C1 N =
200

Midpoint Count

20
6 **

24 24


28 26
**

32 27
***

36 28


40 26
**

44 31
***

48 24


52
8 


Histogram of C2 N = 2000
Each * represents 5 observation(s)

Midpoint Count

20 71
***

22 113
***

24 131
***

26 142
*

28 131
***

30 125
*

32 151
***

34 129
**

36 135
***

38 124
*

40 145
*

42 110
**

44 130
**

46 121
*

48 120


50 122
*

now, i also looked at the pro graphics under each case and found
for n=200, there were about 16 intervals ... and when n=2000, there were
about 31 intervals ... or about twice ... similar to the difference (in
ratio) in the older graphics ... 

help in minitab does not provide any clue about the algorithm on this ...
but clearly, it treats them differently ... but of course, one can change
this to whatever YOU want ... with subcommands

At 11:01 PM 1/4/01 -0500, Jineshwar Singh wrote:
To determine the number of classes
for a histogram, Excel uses square root
of the number of observations. Is it also true for the number of
observations greater than 200, say, for 2000?. Does the MINITAB use the
same
for determining the number of classes for a histogram?
Any help would be appreciated.





=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at

http://jse.stat.ncsu.edu/
=




=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

Number of classes.

[Jineshwar Singh]

To determine the number of classes for a histogram, Excel uses square root
of the number of observations. Is it also true for the number of
observations greater than 200, say, for 2000?. Does the MINITAB use the same
for determining the number of classes for a histogram?
Any help would be appreciated.





=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=