1. Intro Stats Lesson 1.3 B Objectives: SSBAT classify different ways to collect data. SSBAT distinguish between different sampling techniques. Standards: S2.5B

2. Census  A count or measure of an ENTIRE population  This provides complete information but is often costly and difficult to perform

3. Sampling  A count or measure of a PART of a population  More commonly used  The researcher must make sure that the sample used is unbiased – it has to be representative of the entire population. Sampling Error  The difference between the results of a sample and those of the entire population.

4. Biased Sample  A sample in which one or more of the parts of the population are favored over the others.

5. With Replacement  The same person from the population can be picked more than once  They are put back into the mix after they are picked. Without Replacement  Each person can only be picked once  They are not put back into the mix after they are picked

6. Sampling Techniques 1.Random Sample 2.Simple Random Sample 3.Stratified Sample 4.Cluster Sample 5.Systematic Sample 6.Convenience Sample

7. 1.Random Sample  Every member of the population has an equal chance of being selected for the experiment.

8. 2. Simple Random Sample  A sample in which every possible sample of the same size has the same chance of being selected.  Use a random number table or generator Example: There are 345 students enrolled in a statistics course. Their teacher wants to form a sample of 8 students to answer questions to a survey. Select the students who will belong to the simple random sample.  Show how to do in Graphing Calculator

9. 3. Stratified Sample  Used when it is important to have members from each subset of the population  Subsets are called Strata  1 ST : Members of the population are divided into 2 or more subsets (strata) that share a similar characteristic (age, gender, income, etc)  2 ND : A sample is then randomly selected from each of the subsets Example: Collecting information from the households in a given region. It would be important to have members from each Socioeconomic level  Low Income, Middle Income, and High Income

10. 4.Cluster Sample  Use when the population falls into naturally occurring subgroups, each having similar characteristics  The subgroups are called Clusters  To collect a cluster sample, select all of the members in 1 or more of the clusters (don’t choose all of the clusters) Example: If Pennsylvania was the population, the clusters could be each County

11. 5. Systematic Sample  First: Every member of the population is assigned a number  Second: All the members are ordered in some way  Third: A starting number is assigned and then the sample is selected at regular intervals (Every 3 rd person, Every 5 th person, etc)

12. 6.Convenience Sample  Consists only of available members of the population  Includes members that are easily accessed  Often leads to Biased results therefore it’s not recommended to use Example: The first 25 people in line for a concert The top 20 apples in a crate.

13. Pass out Graphic Organizer 1.3 B

14. Examples: Select the Sampling Technique that should be used for each. 1.You assign each student a number and generate random numbers. You then question each student whose number is randomly selected.  Simple Random Sample

15. 2.You select a class at random and question each student in that class.  Cluster Sample (each class is a naturally occurring subgroup or cluster)

16. 3. You divide the student population into groups according to their majors first and then randomly select some students from each major.  Stratified Sample (the population is divided into subsets first)

17. 4. You assign each student in your grade a number and, after choosing a starting number, you question every 10 th student.  Systematic Sample

18. 5.A store manager is checking merchandise as it comes in to assess the quality of the shipment. He checks the top 12 items in each box.  Convenience Sample

19. Voluntary Response Sample  Involves only those who want to participate

20. Homework Page 25 – 27 #2, 5, 7, 9, 17 – 23, 29, 30