5.3: SAMPLING Other types of samples…

Review: Three sample designs covered so far: 1.Simple Random Sample (SRS) 2.Voluntary Response Sample 3.Convenience Sample

Other ways to take samples Example: At a university, there are 1500 professors. However, 1000 are male and 500 are female. To take an accurate sample of the university faculty’s opinions, we decide to take a sample of 100 male professors and 50 female. Their total sample is these 150 professors. Why is this not an SRS? What was their process? Why is this sampling method better than just an SRS?

Stratified Random Sample: (NOT simple random sample) 1)Divide population into groups with something in common (called STRATA) Example: gender, age, etc. 2) Take separate SRS in each strata and combine these to make the full sample - can sometimes be a % of each strata

Try p. 246 #62 BASKETBALL Instructions: 1.Use a TRD and read off 2 digits at a time 2.Assign to each player and ignore 00, Read off 7 numbers and ignore repeats 01 Arenas06 Duncan11 Leslie16 Robinson 02 Billups07 Farmar12 McGrady17 Stoudamire 03 Brand08 Fowles13 Miller18 Taurasi 04 Bryant09 Gasol14 Nowitzki19 Wade 05 Carter10 Iverson15 Parker Line 101:

Try p. 246 #62 GOLF (Use line 103) Instructions: 1.Use a TRD and read off 1 digit at a time 2.Assign 1-9 to each player and ignore 0 3.Read off 3 numbers and ignore repeats 1 Cramer4 Kim7 Singh 2 Els5 Mickelson8 Wie 3 Gulbis6 Prammanasudh9 Woods Line 103:

Try p. 247 #68 (a) First separate the faculty into the 2000 males and 500 females -MALES 1.Use TRD and read off 4 digits at a time 2.Assign the males #0001 – 2000, and ignore 0000, Read off 200 numbers and ignore repeats -Females 1.Use TRD and read off 3 digits at a time 2.Assign the females #001 – 500, and ignore 000, Read off 200 numbers and ignore repeats The total 400 faculty selected are our sample

Systematic Sample: * Example: Interview every 5 th person that walks thru the back door of CB South in the morning. * Example: Write down the type of car in every 3 rd spot in the CB South parking lot. * Randomly picking a first individual, and then selecting every ____ person after that.

Cluster Sample Pick a certain area/part of the population. Try to get every individual in that selection Example: select one lunch period, and talk to everyone at that lunch Census Sample everyone in the entire population.

EXAMPLE: We need to survey a random sample of 30 passengers on a flight from San Francisco to Tokyo. Name each sampling method described below: Pick every 10 th passenger that boards From the boarding list, randomly choose 5 people flying first class, and 25 of the other passengers Randomly generate 30 seat numbers and survey the passengers who sit there Randomly select a seat position (right window, left window, right aisle, etc.) and survey all people in those seats

Questions to ask before you believe a poll: p. 249

Random Rectangles Activity!

Try the following: p. 253 – 256 #77, 78, 80, 83

77) (a) Biased because of undercoverage. You are not able to sample the most expensive seats (b) Sampling error, because it was an error in the WAY you collected your sample 78) 1. Use a TRD and read off 2 digits at a time 2. Assign each person a number 01-30; ignore 00, Read off 4 numbers and ignore repeats # 19, 26, 06,09 Rodriguez, Montoya, Fernandez, Castillo

80) (a) the population is all American college students (b) the list of 340 PSY 001 students (c) If he is trying to conclude about ALL college students, you should not just sample from students in PSY 001. (d) Yes, it is slanted. “fair price to pay” (e) He did not ask students about whether they were in favor of TV commercials. He asked them if they thought commercials were a fair price to pay for watching TV. (f) No, not relevant. The sampling frame does not represent the population.

83) The wording “fight the charges” makes it seem like he is justly charged for a crime and the second question wording of “continue to serve” makes it seem like he should stay in office.

Try p. 255 #81, 86

81) (a) Instructions 1. Use a TRD and read off 4 digits 2. Assign each student a number ; ignore 0000, Read off 250 numbers and ignore repeats (b) - Randomly choose a number from 1 thru once you have that number (like 7 for example), take every 10 th person from that (like 17 th, 27 th, 37 th, etc.)

81) (c) Instructions - Bused 1. Use a TRD and read off 4 digits 2. Assign each student a number ; ignore 0000, Read off 200 numbers and ignore repeats Instructions - Local 1. Use a TRD and read off 4 digits 2. Assign each student a number ; ignore 0000, Read off 50 numbers and ignore repeats (d) stratified. It is a more accurate representation of the population.