AP Statistics
Notes
Name: ____________
Date: ____________
Lesson 1.2B: Quartiles, Percentiles, and Box Plots
Objectives:
M: Find the quartiles Q1 and Q3 for a set of observations.
N:
Give the five-number summary and draw a boxplot; assess center, spread,
O:
symmetry, and skewness from a boxplot. Determine outliers.
Make side-by-side boxplots to compare distributions of quantitative variables.
Vocabulary:
Boxplot
pth Percentile
I.
First quartile
Third quartile
Interquartile range (IQR)
1.5 x IQR Rule for outliers
Constructing a Boxplot (Quantitative variable)
Construct a boxplot for the quantitative variable, “number of contacts
programmed in cell phone,” from the class data set.
1.
Find the percentile rank of ________.
2.
What number of contacts is at the 30th percentile?
3.
Find Q 1 , the median, and Q 3 .
4.
Give the 5-number summary for the “number of contacts” data.
Use the 5-number summary to construct a boxplot.
Min
𝑄1
Med
𝑄3
Max
CUSS
and
BS !!
5. Use the 1.5 x IQR criteria to determine if there are any outliers in the “contacts” data.
6. If you identified any outliers in #5, construct a modified boxplot for the “contact” data.
(Construct it above the original boxplot on the grid on the preceding page.)
II. Comparing Boxplots
1.
Determine the 5-number summary for the female “contacts” data.
Determine the 5-number summary for the male “contacts” data.
2.
Use the 1.5 x IQR to determine if there are any outliers in the female or male
“contacts” data.
3.
Construct parallel boxplots (maybe modified) for the female and male “contacts”
data. Remember to use the same scale on your graphs so the boxplots are
easier to compare.
4.
Compare the female and male “contacts” boxplots. CUSS and BS !!