–every possible sample of size n has an equal chance of being selected –Randomly select subjects Simple Random Sample (SRS) Suppose we were to take an SRS of 100 CHS students – put each students’ name in a hat. Then randomly select 100 names from the hat. Each student has the same chance to be selected! Not only does each student has the same chance to be selected – but every possible group of 100 students has the same chance to be selected! Therefore, it has to be possible for all 100 students to be juniors in order for it to be an SRS!

There are 15 classrooms in the math wing to sample from during 4 th period. Each class has exactly 25 students. A sample of 30 students is chosen by the following procedure: Each of the 15 teachers selects 2 students from his/her classroom to be in the sample by numbering all the students from 1 to 25, then using the TI-84 calculator to randomly select two different numbers between 1 and 25. The 2 students with those numbers are in the sample. Did this procedure give a simple random sample of 30 students from the math wing 4th period? NO! Is the following a SRS??

Cluster vs. Stratified In a cluster sample you randomly select a cluster (usually heterogeneous groups) and sample everyone in that cluster In a stratified sample you divide the population into stratas (usually homogeneous groups) and then randomly select a few from each strata.

1) Suppose your local school district decides to randomly test high school students for attention deficit disorder (ADD). There are three high schools in the district, each with grades 9 – 12. The school board pools all of the students together and randomly samples 250 students. Identify the sampling design SRS

2)The Educational Testing Service (ETS) needed a sample of colleges. ETS first divided all colleges into groups of similar types (small public, small private, etc.) Then they randomly selected 3 colleges from each group. Stratified random sample Identify the sampling design

3) A county commissioner wants to survey people in her district to determine their opinions on a particular law up for adoption. She decides to randomly select blocks in her district and then survey all who live on those blocks. Cluster sampling Identify the sampling design

4) A local restaurant manager wants to survey customers about the service they receive. Each night the manager randomly chooses a number between 1 & 10. He then gives a survey to that customer, and to every 10 th customer after them, to fill it out before they leave. Identify the sampling design Systematic random sampling

5) A statistics teacher wants to know how her students feel about an introductory Stat course. She has 200 students total but doesn’t want to ask them all. She decides to administer a survey to a random sample of students taking the course using the following procedure: Each student is given a number from She then randomly selects 50 numbers using the TI-84 calculator. The students selected get to be in the sample. Identify the sampling design SRS

6) A company packaging snack foods maintains quality control by randomly selecting 10 cases from each day’s production. Then they randomly select 5 bags from each case and inspect then contents. Identify the sampling design Multi-stage sampling

7) There are 10 classrooms in the math wing to sample from during 4 th period. Each class has exactly 20 students. A sample of 30 students is chosen by the following procedure: Each student is given a number and the using a TI-84 calculator 30 numbers are randomly generated. The 30 students with those numbers are in the sample. Identify the sampling design SRS