Frequency Distributions and Statistical Graphs

A frequency distribution is a listing of the observed values and the frequency of each.
you can build a frequency distribution with a class width of one right now.
- Data: 1 1 2 3 3 3 3 4 5 5 5 5 5 6 6 7
- Item Frequency
  
  1 2
  
  2 1
  
  3 4
  
  4 1
  
  5 5
  
  6 2
  
  7 1
- This is nice, but will not render credit in this class.
When we build a frequency distribution
- We will place the data into a number of classes
- Each class has a lower class limit (or the minimum value of the data in that class)
- Each class has an upper class limit (or the maximum value of the data in that class.
- The class width is the difference between any two consecutive lower class limits.
- The Class Mark for any class is the average of the upper and lower class limits for that class.
To create a frequency distribution
- You are normally given the first lower class limit.
- And either the next lower class limit, the first upper class limit or the class width.
  - From this information we can calculate the other values.
- Construct each class
- Count the data that appears in each class.
Rules
- The classes must be the same width.
- The classes must not overlap.
- Each piece of data must belong to only one class.
Building histograms and frequency polygons.
- Label the x axis with the class mark for each class.
- Label the y axis with the frequencies.
- For a histogram
  - Draw a polygon for each class centered on the class mark.
- For a frequency polygon
  - Place a dot at (class mark, frequency) for each class.
  - Place a dot at (first lower mark-width,0) (last upper mark + width,0)
  - Draw lines between the dots.
For a stem and leaf display
- All data values must use the same number of digits.
- List all of the most significant digits in order (stems).
- List the corresponding next digit next to each stem (leaves).
- Provide a key in the form of s|l = sl
Do problem 9 page 743
Do problems 29 and 30 page 745
Do problem 31 page 745

Item	Frequency
1	2
2	1
3	4
4	1
5	5
6	2
7	1