Chapter 2: Types of Data and DisplaysChapter 2: Types of Data and Displays

Collected data may be classified into one of Collected data may be classified into one of two broad categories:two broad categories:

1.1. Qualitative data – consists of Qualitative data – consists of observations which can be placed into observations which can be placed into categories. The categories describe categories. The categories describe some attribute or quality of interest. some attribute or quality of interest.

Examples:Examples: College MajorCollege Major

Favorite ColorFavorite Color

Political Party PreferencePolitical Party Preference

Chapter 2: Types of Data and Displays Chapter 2: Types of Data and Displays

(Continued)(Continued)

2.2. Quantitative data – consists of Quantitative data – consists of observations that observations that measuremeasure some some quantity of interest. Each observation is quantity of interest. Each observation is a number. a number.

Examples:Examples:

College GPACollege GPA

Number of Emergency Room PatientsNumber of Emergency Room Patients

Price of gasoline in the areaPrice of gasoline in the area

Chapter 2: Quantitative vs Qualitative DataChapter 2: Quantitative vs Qualitative Data

It is tempting to say numbers represent It is tempting to say numbers represent quantitative data, while words represent quantitative data, while words represent qualitative data. qualitative data.

What does the “205” represent in STA 205? What does the “205” represent in STA 205? Does it really mean it is a harder course Does it really mean it is a harder course than all MAT/STA courses with lower than all MAT/STA courses with lower numbers? numbers?

This is a scheme to categorize MAT/STAThis is a scheme to categorize MAT/STA

classes. It does nothing except categorizeclasses. It does nothing except categorize

the course. It the course. It does not measuredoes not measure

anything, right? anything, right?

Self-Quiz for PracticeSelf-Quiz for Practice

Classify each set of data as either Classify each set of data as either quantitative or qualitative data:quantitative or qualitative data:

1.1. The heights of current STA 205 studentsThe heights of current STA 205 students

2.2. The GPAs of current STA 205 studentsThe GPAs of current STA 205 students

3.3. The favorite ice cream flavors of all U.S. The favorite ice cream flavors of all U.S. senatorssenators

4.4. The home telephone numbers for all The home telephone numbers for all players on the Cincinnati Reds baseball players on the Cincinnati Reds baseball teamteam

5.5. Gas mileages for the cars parked next to Gas mileages for the cars parked next to this buildingthis building

Answers to Self-QuizAnswers to Self-Quiz

1.1. heights - Quantitativeheights - Quantitative

2.2. GPAs - QuantitativeGPAs - Quantitative

3.3. ice cream flavors - Qualitativeice cream flavors - Qualitative

4.4. telephone numbers - Qualitativetelephone numbers - Qualitative

5.5. Gas mileages – QuantitativeGas mileages – Quantitative

Notice in 1, 2, and 5 the numbers obtained Notice in 1, 2, and 5 the numbers obtained measure something. Although # 4 gives measure something. Although # 4 gives a “number”, it locates a place but does a “number”, it locates a place but does not measure anything. not measure anything.

Brief CommentsBrief Comments

Presenting and Analyzing the two types of Presenting and Analyzing the two types of data require different techniques. data require different techniques.

Most of the discussion in this class focuses Most of the discussion in this class focuses on quantitative data. However, we will on quantitative data. However, we will mention techniques of inference for mention techniques of inference for qualitative data also (proportions, chi-qualitative data also (proportions, chi-square test of contingency tables)square test of contingency tables)