Sept 13, 2013
Chapter 2, Section 2, Pages 18-29
Evidence of an Association (Dependence)
• Two variables have an association, or relationship, if a particular value for one
variable is more likely to occur with certain values of the other variable. (i.e The
distribution of one variable is not the same for all categories of the variable)
o If a pregnant woman who consumes >200 mg of caffeine is more likely o
have a miscarriage than woman consuming less caffeine, that is going to
suggest an association.
• Two variables have an association, or relationship, if two or more rows in the
contingency table have different distributions of row percentages, or equivalently
if two or more columns have different distributions of column percentages (i.e the
conditional distributions are not the same)
Admission to Magnet Schools (Exercise 2.15, 2.16)
• AN article in the Winter 2003 issue of Chance magazine on the Houston
Independent School District’s magnet school programs. Of the 1755 qualified
applicants, 931 were accepted, 298 were waist listed and 526 were turned away
for lack of space. Find the relative frequency of distribution of the decisions
made, and write a sentence describing it.
o 931/1755 = .530, 298/1755 = .170 , 526/1755 = .30
relative frequency is percentage of each category.
o Among the 1755 qualified applicants, 53% were accepted, 17% were wait
listed and 30% were turned away due to lack of space.