Populations & Samples

1. Populations & Samples January 04, 2013

2. Riddle Me This.. • What is in seasons, seconds, centuries, and minutes but not in decades, years, or days? • The letter “n” • seasoNs • secoNds • ceNturies • miNutes

3. Kick Off • Evaluate the expression using the correct order of operations. 9 + 3(4 - 2) – 8 / 2 • 11

4. Essential Question • How can I compare and analyze sampling methods? • BrainPop: Statistics

5. Objective • Learnto compare and analyze sampling methods.

6. Vocabulary • Population • The entire group of objects or individuals considered for a survey • Sample • A part of a population • Random Sample • A sample in which each individual or object in the entire population has an equal chance of being selected • Convenience Sample • Sampling the most available subjects in a population to obtain quick results • Biased Sample • A sample that does not fairly represent the population

7. Populations and Samples In 2002, there were claims that Chronic Wasting Disease (CWD), or Mad Elk Disease, was spreading westward across North America. In order to verify claims such as these, the elk population had to be tested. When information is gathered about a group, such as the elk in North America, the entire group is called the population. Because testing each member of a large group can be difficult or impossible, researchers often study a part of the population, called a sample.

8. Helpful Hint A random sample is more likely to be representative of a population than a convenience sample is. Populations and Samples For a random sample, members of the population are chosen at random. This gives every member of the population an equal chance of being chosen. A convenience sample is based on members of the population that are readily available, such as 30 elk in a wildlife preservation area.

9. Populations and Samples Additional Example 1: Analyzing Sampling Methods Determine which sampling method will better represent the entire population. Justify your answer. Jon’s sample is a random sample, giving every band member equal chance to be surveyed, so it is the better method.

10. Populations and Samples Check It Out: Example 1 Determine which sampling method will better represent the entire population. Justify your answer. Ferdinand’s sample is a random sample, giving results that better represent the entire swimming team, so it is the better method.

11. Populations and Samples A biased sample does not fairly represent the population. A study of 50 elk belonging to a breeder could be biased because the breeder’s elk might be less likely to have Mad Elk Disease than elk in the wild.

12. Populations and Samples Additional Example 2: Identifying Potentially Biased Samples Determine whether each sample may be biased. Explain. A. The mayor surveys 100 supporters at a rally about the most important issues to be addressed by the city council. The sample is biased. The supporters may have different ideas than those not at the rally. B. The principal sends out questionnaires to all of the students to find out what kind of music students prefer at dances. The sample is random. The students all have a chance to respond.

13. Populations and Samples Check It Out: Example 2 Determine whether each sample may be biased. Explain. A. The owner of a record shop surveys only customers over the age of 18 who shop at his store. This is not random. Customers under the age of 18 do not have a chance of being chosen. B. The teacher writes the name of each student on a piece of paper and questions the students whose names are drawn. This sampling method is random. Each student has an equal chance of being chosen.

14. Populations and Samples Additional Example 3: Verifying Claims Based on Statistical Data A principal of a school with 1,500 students estimates that about 400 students will attend a band festival on Saturday. A random sample of 25 students showed that 6 of them will attend. Determine whether the principal’s estimate is likely to be accurate. Set up a proportion to predict the total number of students that will attend. Students attending sample # of Students sampled Students attending Student Population =

15. Populations and Samples Additional Example 3 Continued Let x represent the number of actual students attending the band festival. 6 25 x 1500 = 6 • 1500 = 25 • x The cross products are equal. Multiply. 9000 = 25x 9000 25 25x 25 Divide each side by 25 to isolate x. = 360 = x The estimate is not accurate because the data shows that 360 students are likely to attend.

16. Populations and Samples Check It Out: Example 3 The owner of a large chain restaurant with 1,200 employees estimates that about 250 employees will ask for winter vacation. A random sample of 40 employees showed that 8 of them will ask for the time off. Determine whether the owner’s estimate is likely to be accurate. Set up a proportion to predict the total number of students that will attend. Employees surveyed for time off # of Employees surveyed Employees asking for time off Total # of Employees =

17. Populations and Samples Check It Out: Example 3 Continued Let x represent the number of actual employees asking for time off. 8 40 x 1200 = 8 • 1200 = 40 • x The cross products are equal. Multiply. 9600 = 40x 9600 40 40x 40 Divide each side by 40 to isolate x. = 240 = x The estimate is accurate because the data shows that 240 employees will ask for time off.

18. Populations and Samples Lesson Quiz: Part I 1. Determine which sample better represents the entire population. b a. A TV ratings service is surveying residents of Orlando who bought TVs in the last month about their favorite TV show. b. A TV ratings service called residents of Orlando randomly selected from the phone directory to conduct a survey about their favorite show.

19. Populations and Samples Lesson Quiz: Part II 2. Determine whether each sample may be biased. Explain. a. A convenience store surveys customers one morning to determine what products they may like the store to stock. b. Each student’s name is written on a slip of paper and placed in a box. One slip of paper is selected to determine the student to be the homeroom representative. Biased; at other times of the day, customers may have different preferences. Not biased; the sample is random.

20. Populations and Samples Lesson Quiz: Part III 3. A local middle school has 2500 students. Morgan interviewed 75 of the students about their library habits. She found that 45 of the students checked out a book weekly. Predict the number of students likely to check out books weekly. 1500

21. Let’s Practice • With your elbow partner, complete 7-8 Reteach and 7-8 Reading Strategies. • If you finish, raise your hand for me to check your work. If your work is accurate, you may begin on your homework. • HW: WB 7-8, page 65 • Last five minutes: Continue to work while I stamp agendas.

22. Essential Question • What factors affect the outcomes of a survey or study? Why is this important to me? • How do you select a valid sample to survey or study?

23. Frameworks Task • Individually and silently, work for 10 minutes on the Is It Valid? Task provided. • After 10 minutes, you may discuss with your elbow partner for an additional 10 minutes. • If needed, you will be given 5 additional minutes of individual work time to complete the task. • Write your name on the paper and turn in to the basket.

24. Puzzles, Twisters, & Teasers • Tyler surveys 60 people at a high school football game to find out which high school sports team is most popular. O A biased not biased • A computer manufacturer randomly calls 150 people who called its help line and surveys them to determine if they were satisfied with the help they received. MN biased non biased

25. Puzzles, Twisters, & Teasers • Margie surveys 12 of her friends to determine what percentage of students participate in after-school clubs. F D random sample convenience sample • Tamira surveys 50 riders on one commuter train to determine whether riders on all trains in the system think that the on-time performance is adequate. K A biased non biased

26. Puzzles, Twisters, & Teasers • Sam calls every sixth student on a high school attendance list and surveys the students to determine their favorite subject. MR random sample convenience sample Write the circled letters above the problem numbers to solve the riddle. What is the difference between dinosaurs and dragons? Dinosaurs ____ ____ ____ ____ T S ____ ____ ____ E. 3. 1. 2. 1. 5. 1. 4.

27. Homework • For the rest of the period, you may work quietly with your elbow partner on your homework. • HW: 7-8 Problem Solving • Last five minutes: Continue to work while I stamp agendas.