If you did not turn in the sheet from yesterday, get it out now.

If you did come get it from the front table

Jan. 27th, 2015

Vocabulary• Categorical Variables - represent types of data

which may be divided into _______________. Examples of categorical variables are race, sex, age group, and educational level.

• • Contingency Table (or two-way frequency

table) - table in which __________________ correspond to two variables. (One variable is used to categorize rows, and a second variable is used to categorize columns.)

groups

frequencies

Ex 1) The following contingency table displays crime data,

a) How many crimes were committed by a stranger?

b) How many crimes were robberies?

Ex 1) The following contingency table displays crime data,

c) How many crimes were robberies were committed by acquaintances or relatives?

d) How many crimes were committed all together?

Ex 2) Mr. Smith keeps track of his students’ homework completion. He keeps track of how many boys and girls do not complete their homework. He puts students who don’t

complete their homework into two categories: first-time offenders and repeat offenders. He uses a table to keep track of the results.

Total

Total

a). In one month 36 girls and 12 boys did not do their homework for the first time. 12 girls and 30 boys did not do their homework again. Put these figures in your table.

b). How many students did not complete all of their homework assignments this month? c). What percentage of the students who did not complete their homework were boys who were First-Time Offenders?

d). Are boys or girls more likely to not complete their homework? Explain your reasoning.

Contingency Tables Part 2

Jan. 27th, 2015

Vocabulary

• Joint Frequency – frequencies in the ______ of the table

• Marginal Frequency – entries in the “Total” ____ and “Total” ________

• Relative Frequency Distribution– The relative frequency distribution provides the ratio of occurrences in each _______ to the ______ number of occurrences. The relative frequencies in the body of the table are called __________ frequencies.

body

rowcolumn

entry total

conditional

Ex 1). The following contingency table displays crime data,

Homicide Robbery Assault TotalsStranger 12 379 727 1118Relative or Acquaintance

39 106 642 787

Totals 51 485 1369 1905

a). Identify the joint frequencies. b). Identify the marginal frequencies.

Ex 2). Use the table in example 1 to construct the relative frequency distribution.

Homicide Robbery Assault Totals

Stranger

Relative or Acquaintance

Totals

Ex 3). A community outreach director wants to plan special summer activities for its members. He posts a survey on the local newspaper’s website to gather information on the favorite activities of the community members. Participants identified their age and then chose from four given activities. The responses gathered from the survey are shown.

Sports Movies Reading Walking Total18 and under 20 30 22 8 Ages 19-50 10 32 25 43 50 and older 5 20 35 30 Total

a). Use the table to construct the relative frequency distribution.

Sports Movies Reading Walking Total18 and under Ages 19-50 50 and older Total

b). Which age group made up the smallest percent of people surveyed?

c). Which activity was preferred by the largest percent of people surveyed?