Stem and Leaf and Scatter Plots

Date: 10/13/98 at 23:01:44
From: Kyle Curre
Subject: Scatter plots and stem and leaf plot graphs

Hi. I am desperately trying to find out what stem and leaf and 
scatter plots are. I have searched everywhere for an explanation of 
what they are and how to make them. I am doing a math project for 
Pre-Algebra, and I have to use stem and leaf and scatter plots. My 
teacher wants us to be resourceful and find out all the information 
we need ourself. 

Thanks again,
Kyle Curre

Date: 10/14/98 at 09:20:13
From: Doctor Statman
Subject: Re: Scatter plots and stem and leaf plot graphs

Dear Kyle,

A stemplot is a graphical display that is used to represent one column 
of data. A scatterplot represents the relation between two columns.

Here are two examples. Suppose I had one column of data that contained
the following numbers:

   10 11 15 26 28 28 29 31 31 32 37 38

Look at the number 10, and think about it as a stem (1) plus a leaf 
(0). So 10 becomes 1 | 0, writing the stem, then a bar, then the leaf.  
Look at the 11. The 11 becomes 1 | 1, with the same stem as the 10.  
So you can think of the 10 and the 11 as two leaves on the same stem 
like this:

   1 | 01

Now I'll put the rest of the stems and leaves for these numbers 
together:

   1 | 015
   2 | 6889
   3 | 11278

Can you see the stems for the 10's, 20's, and 30's? Can you see how 
many 28's are in the data? Do you see how to break the numbers up into 
stems and leaves?  Pretty cool, right?

Now a scatterplot is different - you need two columns of data.
Here are the heights and weights of the people in my family:

             Height     Weight
            (inches)   (pounds)
   Dad         73        185
   Mom         65        125
   Kid 1       50         55
   Kid 2       43         45
   Kid 3       38         33
   Kid 4       27         24

I can plot these two columns against each other in a scatterplot. I 
made this one in a computer package called Minitab.

Scatterplot


         -
         -
      180+                                                    + Dad
         -
Weight   -
         -
         -
      120+                                            + Mom
         -
         -
         -
         -
       60+                             +
         -                      +
         -                 +
         -      +
         -
           --------+---------+---------+---------+---------+--------  
      Height      30        40        50        60        70

Do you see how there are six people in my family and six points (+) on 
the scatterplot? Each plus sign is one person - I find their height on 
the horizontal or x axis, and then I find their weight on the vertical 
or y axis, and I put a + sign where they meet.

If you need more help, I suggest you visit a site like this one by Rex 
Boggs called Exploring Data, from Queensland, Australia:

   http://exploringdata.cqu.edu.au/   

It has some good stuff about stemplots and scatterplots.

I hope this helps. Good luck with your project.

Statistically yours,

- Doctor Statman, The Math Forum
  http://mathforum.org/dr.math/