5.3: sampling other types of samples…. review: three sample designs covered so far: 1.simple...

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 #62BASKETBALLInstructions: 1. Use a TRD and read off 2 digits at a time2. Assign 01-19 to each player and ignore 00,20-993. Read off 7 numbers and ignore repeats

01 Arenas 06 Duncan 11 Leslie 16 Robinson02 Billups 07 Farmar 12 McGrady 17 Stoudamire03 Brand 08 Fowles 13 Miller 18 Taurasi04 Bryant 09 Gasol 14 Nowitzki 19 Wade05 Carter 10 Iverson 15 Parker

Line 101: 19223 95034 05756 28713 96409 1251 42544 82853

73676 47150 99400 01927 27754 42648 82425 36290

Try p. 246 #62GOLF (Use line 103)Instructions: 1. Use a TRD and read off 1 digit at a time2. Assign 1-9 to each player and ignore 03. Read off 3 numbers and ignore repeats

1 Cramer 4 Kim 7 Singh2 Els 5 Mickelson 8 Wie3 Gulbis 6 Prammanasudh 9 Woods

Line 103:

45467 71709 77558 00095 32863 29485 82226 90056

Try p. 247 #68 (a)First separate the faculty into the 2000 males and 500 females- MALES1. Use TRD and read off 4 digits at a time2. Assign the males #0001 – 2000, and ignore 0000,

2001-99993. Read off 200 numbers and ignore repeats- Females1. Use TRD and read off 3 digits at a time2. Assign the females #001 – 500, and ignore 000,

501-9993. Read off 200 numbers and ignore repeats

The total 400 faculty selected are our sample

Systematic Sample:

* Example: Interview every 5th person that walks thru the back door of CB South in the morning.

* Example: Write down the type of car in every 3rd 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 10th 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, 31-99

3. 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 0001-3500; ignore 0000, 3501-9999


(b) - Randomly choose a number from 1 thru 10.

- once you have that number (like 7 for example), take every 10th person from that (like 17th, 27th, 37th, etc.)

81) (c) Instructions - Bused




Instructions - Local




(d) stratified. It is a more accurate representation of the population.

5.3: sampling other types of samples…. review: three sample designs covered so far: 1.simple...

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