1. 12-5 Samples and Surveys

2. Quantitative: data measure quantities and can be described numerically Example: test scores, ages, time, weight Qualitative: data name qualities and can be words or numbers Example: Sports, zip codes, hair color

3. Problem 1: Classifying Data
Is each set Qualitative or Quantitative?
Favorite Movies
Number of students in different school who take Spanish
Football Jersey Numbers

4. Univariate: a set of data that uses only one variable Bivariate: a set of data that uses two variables

5. Problem 2: Identifying Types of Data
Is each data set univariate or bivariate?
The atomic weights of the elements in the periodic table
The edge lengths and volumes of cubes
Heights and weights of mammals
The cost of Internet service from several different providers

6. Populations: the entire group that you want information about Sample: When a population is too large to survey, statisticians survey a part of it to find characteristics of the whole. This part is called the Sample

7. NAME
SAMPLING
METHOD
EXAMPLE
Random
Survey a population at random
Survey people whose names are drawn from a hat
Systematic
Select a number n at random. Then survey the nth person
Select the number 5 at random. Survey every fifth person
Stratified
Separate a population into smaller groups, each with a certain characteristic. Then survey at random within each group.
Separate a high school into 4 groups by grade level. Survey a random sample of students from each grade

8. Problem 3: Choosing a Sample
You want to find how many DVDs students at your school rent in a month. You interview every tenth teenager you see at a mall. What sampling method are you using? Is this a good sample

9. You revise your plan and interview all students leaving a school assembly who are wearing the school colors. Will this plan give a good sample? Explain.

10. BIAS: when a survey contains assumptions that may or may not be true
BIAS: when a survey contains assumptions that may or may not be true. It can influence opinion and can make one answer seem better than another.

11. Problem 4: Determining Bias in a Survey
A reporter wants to find out what kinds of movies are most popular with local residents. The reporter asks “Do you prefer exciting action movies or boring documentaries?” Is the question biased? Explain.