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

Review: Three sample designs covered so far: Simple Random Sample (SRS) Voluntary Response Sample 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) 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: Assign 01-19 to each player Use a TRD and read off 2 digits at a time Ignore 00,20-99, and repeats Read off 7 numbers 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: 19223 95034 05756 28713 96409 1251 42544 82853 73676 47150 99400 01927 27754 42648 82425 36290

Try p. 246 #62 GOLF (Use line 103) Instructions: Use a TRD and read off 1 digit at a time Assign 1-9 to each player and ignore 0 Read off 3 numbers and ignore repeats 1 Cramer 4 Kim 7 Singh 2 Els 5 Mickelson 8 Wie 3 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 MALES Use TRD and read off 4 digits at a time Assign the males #0001 – 2000, and ignore 0000, 2001-9999 Read off 200 numbers and ignore repeats Females Use TRD and read off 3 digits at a time Assign the females #001 – 500, and ignore 000, 501-999 The total 400 faculty selected are our sample

Systematic Sample: * Randomly picking a first individual, and then selecting every ____ person after that. * 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.

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

Random Rectangles Activity!