Other Sampling Methods I can distinguish a SRS from a stratified random sample or cluster sample. I can give advantages and disadvantages of each sampling method. Other Sampling Methods I can distinguish a SRS from a stratified random sample or cluster sample. I can give advantages and disadvantages of each sampling method. 4.1 b h.w: p 227: odd

Review SRS Recall: Individuals are selected so that all possible combinations of individuals have an equal chance to be in the sample. Individuals are selected so that all possible combinations of individuals have an equal chance to be in the sample. Its very difficult to obtain an SRS from the population of interest. Its very difficult to obtain an SRS from the population of interest.

Is this an SRS? The dean would like to give a survey to CLC students. He has a list of the 1,600 students at Central. The dean selects a sample of 200 students by randomly selecting 50 students from each class. (discuss with partner) The dean would like to give a survey to CLC students. He has a list of the 1,600 students at Central. The dean selects a sample of 200 students by randomly selecting 50 students from each class. (discuss with partner) Every possible sample of 200 must have an equal chancre of being selected. Every possible sample of 200 must have an equal chancre of being selected. 25 Fresh, 70 Soph, 30 Junior, 75 senoirs npt possible. NOT a SRS. 25 Fresh, 70 Soph, 30 Junior, 75 senoirs npt possible. NOT a SRS.

Labeling Review Number of digits must match all units. Number of digits must match all units. 01 is different than 1, so for hw, 01 – 30 ok for students and 0-9 ok for teachers. 01 is different than 1, so for hw, 01 – 30 ok for students and 0-9 ok for teachers. If you have to pick 50 from 4000, must label with 4 digits. If you have to pick 50 from 4000, must label with 4 digits. Notes: the more digits, the longer it takes to pick off of table B. Better to use 0 -9 than Notes: the more digits, the longer it takes to pick off of table B. Better to use 0 -9 than

Random Sampling Helps us to make generalizations about a population without bias. Helps us to make generalizations about a population without bias. Is the foundation for many of the inference procedures that we will use. Is the foundation for many of the inference procedures that we will use.

Systematic Random Sample The first individual is chosen at random; The first individual is chosen at random; then a system or rule is used to choose all other individuals. Example: Obtain an alphabetized list of all students at CLCHS. (System) Choose first person randomly then every 5th person on the list. Example: Obtain an alphabetized list of all students at CLCHS. (System) Choose first person randomly then every 5th person on the list. System must cover the whole population! System must cover the whole population!

Stratified Random Sample Divide the population into groups of similar individuals called strata; then choose a SRS in each group to form the full sample Divide the population into groups of similar individuals called strata; then choose a SRS in each group to form the full sample Example: Divide all of the students at CLCHS into four groups: freshmen, sophomores, juniors, and seniors; Example: Divide all of the students at CLCHS into four groups: freshmen, sophomores, juniors, and seniors; then choose a SRS from each grade level.

If the individuals in each stratum are less varied from the population as a whole, a stratified random sample can produce better information about the population than an SRS of the same size. If the individuals in each stratum are less varied from the population as a whole, a stratified random sample can produce better information about the population than an SRS of the same size.

Multistage Sample Select several groups; within each group, Select several groups; within each group, select a subgroup; within each subgroup select individuals for the sample. Example: Example: Select several departments within the school (Math, English, Art). Within each of those departments, select several teachers. Choose several students within each class.

Cluster Sample Select several groups; within each group, Select several groups; within each group, select several subgroups; within each subgroup for the sample. select ALL individuals for the sample. Example: Example: Select several departments within the school (Math, English, Art). Within each of those departments, select several teachers. Choose ALL students in each class.

Example: Sampling at School The student council wants to conduct a survey during the first five minutes of an all-school assembly in the auditorium about the use of the school library. They would like to announce the results of the survey at the end of the assembly. The student council president asks your statistics class to help carry out the survey. The student council wants to conduct a survey during the first five minutes of an all-school assembly in the auditorium about the use of the school library. They would like to announce the results of the survey at the end of the assembly. The student council president asks your statistics class to help carry out the survey. Problem: There are 800 students at the assembly. Note that students are seated by grade level and that seats are numbered from 1 – 800. Problem: There are 800 students at the assembly. Note that students are seated by grade level and that seats are numbered from 1 – 800. Randomly selected groups will report out to the class. Randomly selected groups will report out to the class.

Example: Sampling at a School Assembly Describe how you would use the following sampling methods to select 80 students to complete a survey. (a) Simple Random Sample (b) Stratified Random Sample (c) Cluster Sample