1. Other types of samples…
5.3: SAMPLING
Other types of samples…

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

3. 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?

4. This is not an SRS because they do not put all people into one group and randomly select from that. They break them up into two groups and select some from each group. An SRS does not take into account a variable like Gender.
Also, an SRS gives each person an equal chance of being selected. This does not. In this sample, the males have a 1/1000 chance but each female has a 1/500 chance.
This is better because its more representative of the population. The population has more males in it, and this sampling method allows the sample to have the same percent of males as the population.

5. Stratified Random Sample:
(NOT SRS)
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

6. Try p. 246 #62 BASKETBALL Instructions: Assign 01-19 to each player
Use a TRD and read off 2 digits at a time
Ignore 00, 20-99, and repeats
First 7 numbers are our sample
01 Arenas
06 Duncan
11 Leslie
16 Robinson
02 Billups
07 Farmar
12 McGrady
17 Stoudamire
03 Brand
08 Fowles
13 Miller
18 Taurasi
04 Bryant
09 Gasol
14 Nowitzki
19 Wade
05 Carter
10 Iverson
15 Parker
Line 101:
19, 05, 13, 14, 15, 09, 01 =
Wade, Carter, Miller, Nowitski, Parker, Gasol, Arenas

7. Try p. 246 #62 GOLF (Use line 103) Instructions:
Label each golfer with number 1 – 9
Use TRD, line 103, read every 1 digit
Ignore 0 and repeats
First 3 numbers are our sample
1 Cramer
4 Kim
7 Singh
2 Els
5 Mickelson
8 Wie
3 Gulbis
6 Prammanasudh
9 Woods
Line 103:
4, 5, 6 = Kim, Mickelson, Prammanasudh

8. Try p #68 (a)
Use Line 122 for females
Use line 105 for males

9. Try p #68 (a)
First separate the faculty into the 2000 males and 500 females
MALES
Assign the males #0001 – 2000
Use TRD, read across every 4 digits is a male
Ignore 0000, and repeats
First 200 numbers are our sample (line 105)
#0769, 1481, 1315, 0094, 0720

10. FEMALES
Label the females #001 – 500
Use TRD, read across, every 3 digits is a female
Ignore 000, and repeats
First 200 numbers are our sample (line 122)
#138, 159, 052, 087, 359
The total 400 faculty selected are our sample

11. Systematic Sample:
Randomly picking a first individual, and then selecting every ____ person after that.
Good for situations where you do not know your population ahead of time
* 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.

12. 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
Gather info from everyone in the entire population.

13. 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

14. SYSTEMATIC STRATIFIED SRS CLUSTER
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:
SYSTEMATIC
Pick every 10th passenger that boards
From the boarding list, randomly choose 5 people flying first class, and 25 of the other passengers
STRATIFIED
Randomly generate 30 seat numbers and survey the passengers who sit there
SRS
Randomly select a seat position (right window, left window, right aisle, etc.) and survey all people in those seats
CLUSTER

15. Random Rectangles Activity!