1. Displaying Quantitative Data
Chapter 4
Displaying Quantitative Data

2. I. Types of displays
Dot plots – plots a ‘dot’ for each case against a singe axis.
Make each dot the same size
Create a key if the dot stands for more than one unit.
Ex. How many siblings do you have?

3. B. Stem and Leaf plots
Gives a picture of the distribution while including the actual numerical values in the graph.
Stem is all of the number except the final digit. Leaf is final digit.
Write stems in vertical column w/ smallest at the top (Do Not Skip any Stems!!)
May want to split the stems to see the distribution better.
Write each leaf in the row to R of stem in increasing order from L to R.
Provide a key that explains in context what the stems and leaves represent.

4. B. Stem and Leaf plots Example. How many pairs of shoes do you own?
Number of Shoes owned by Stat females. 50 26 31 57 19 24 22 23 38 13 34 30 49 15 51

5. Example Number of Shoes owned by Stat males. 14 7 6 5 12 38 8 10 11 422 35
Back-to-back stemplot is good for comparing two groups of the same
Variable.

6. C. Histograms
Distribution of one quantitative variable that divides the range of data into classes of equal width.
Each bin or class includes the 1st number and goes up to but does not include the last.
Y-axis can be the frequency or relative frequency
No spaces between groups.

7. II. Describing Distributions
Shape
Modes – how many peaks or bumps there are
Uniform – no peaks
Unimodal – one peak
Bimodal – two peaks
Multimodal- more than two peaks.
Symmetry
Symmetric – equal on both sides of the center
Skewed R – tail on R side
Skewed L – tail on L side

8. II. Describing distributions
Center – the place on the graph that would divide the area of the two halves equally.
Mean – used when shape is symmetric or uniform
Median – used when shape is skewed.
Spread – how far away the data is from the center (variability). Calculate the Range.
Outliers and Gaps – observation that differ from the pattern.