Plots

Most plots may be produced by choosing summary from the analysis menu. Some plots (like residual plots) are produced in the regression module. Here is how the summary page looks like after the Height-Weight data is entered.

The following graphs are produced in the summary module by choosing the variable(s) and clicking on the name of the plot. (We will only list those that are used in the course.) As illustrations we will give plots of the variable Weight in the Height-Weight data.

• Histograms
• Boxplots
• Stem and Leaf Plots

Rweb:> stem(Weight)  
 
  The decimal point is 1 digit(s) to the right of the | 
 
  16 | 0 
  18 | 55 
  20 | 589 
  22 | 2550

• Scatterplots - at least two variables have to be selected for a scatterplot to be produced. The scatterplot of Height vs Weight is
• Comparison Boxplots - Comparison boxplots are produced by adding an auxilliary variable when the data is entered. For example, if we need a comparison boxplot of X and Y in the following data set

      x    y
      74   73
      75   78
      77   76
      73   72
      69   65
      73   64
      78 
      76 
      77 
      78

we need to stack the two columns into one column and add a variable indicating whether the value is a X or a Y. Let's use "0" for X and "1" for Y. The data entered will be as follows.

      xy   ind
      74   0
      75   0
      77   0
      73   0
      69   0
      73   0
      78   0
      76   0
      77   0
      78   0
      73   1
      78   1
      76   1
      72   1
      65   1
      64   1

The variables "xy" and "ind" will now show in the summary module. Choose "xy" and split boxplot on "ind". Here is what the choices should look like.
Here is what the comparison boxplot looks like.

2000-08-21