1. Displaying Distributions – Quantitative Variables
Lecture 17
Secs – 4.4.2
Mon, Feb 16, 2004

2. Frequency Plots
Frequency Plot – A display of quantitative data in which X’s are drawn over the scale to represent the values.
Draw the real line.
Mark the minimum and maximum values.
Label the values on the scale, as on a ruler.
Mark at regular intervals.
For each data value, draw an X over that value on the scale.

3. Let’s Do It! Let’s do it! 4.10, p. 210 – Random Number Generator.
Use the shortcut on p. 211.
What kind of distribution do you expect to see?
Describe the distribution that you obtained.
Was it exactly what you expected?

4. Let’s Do It!

5. Shapes of Distributions
One reason to make a frequency distribution is that we are interested in the shape of the distribution.
The shape will show important characteristics of the data.

6. Shapes of Distributions
Symmetric – The left side is a mirror image of the right side.
Unimodal – A single peak, showing the most common values.
Bimodal – Two peaks.
Uniform – All values have equal frequency.
Skewed – Stretched out more on one side than the other.

7. Shapes of Distributions
In a unimodal distribution, the values are clustered near the mode.
In a uniform distribution, there is no clustering.
In a distribution that is skewed to the right, there are more extreme values on the right than on the left.

8. Shapes of Distributions
What shape would you expect a distribution of random numbers to have? Why?
What shape would you expect a distribution of household incomes to have? Why?
What shape would you expect a grade distribution to have?
If a grade distribution were bimodal, what would that indicate?

9. Assignment
None.