Honors Statistics Aug 23-8:26 PM Daily Agenda 3. Check homework C4#2 Aug 23-8:31 PM 1
Mar 12-12:06 PM Apr 6-9:53 AM 2
All the artifacts discovered at the dig. Actual Population - Due to the random sampling... All the artifacts discovered at the dig. The 2% of the artifacts randomly chosen from those discovered at the dig. Oct 26-2:42 PM The 1000 envelopes stuffed by the automated machine each hour. Actual Population - Due to the random sampling... All of the 1000 the envelopes. The 40 envelopes sampled at random from the Oct 26-2:55 PM 3
The 45,000 people who made credit card purchases at the department store. Actual Population - Due to the random sampling... All the 45,000 people. Sample - Sadly only the 137 people who returned the survey. BIAS SAMPLE WHY? Oct 26-2:56 PM I am not convinced that a majority of the voters oppose the bill. This is a voluntary sample of her constituents. I would explain to the congresswoman that because of the voluntary nature of the sample there is a bias present. Usually people with strong opinions are the ones motivated to write to their representatives. This sample systematically favors the "oppose" opinion and should not be used to judge the true beliefs of her constituents. Oct 26-2:56 PM 4
This is a voluntary response sample and it will over represent the opinions of those who feel most strongly about the issue being surveyed. Perhaps it was a poll posed just after a woman's professional sports win, a very exciting game so many were thinking about this event and thus in favor of equal pay. Oct 26-2:56 PM This is a convenience sample and it will represent the opinions of those who were If it was during daytime shopping hours then it could over-represent those who do not have a job and have more time to shop than those who are employed. Oct 26-2:56 PM 5
This is a convenience sample and it will represent the opinions of those who were available for the survey, the students who were first to arrive at school. This sample is biased because it will over represent the students who arrived at school first. Perhaps these students needed to get up earlier than the rest and so they did not get as much sleep than the others. 7.2 is less than the average. Oct 26-2:56 PM This is a voluntary response sample. This sample is biased because it will over represent those with strong opinions on the cell phone issue. Probably people who have been in an accident caused by cell phone use. I believe that 85% is probably higher than the true population percent of all adults who believe that cell phone used while driving should be banned. Sadly, many people still use their cell phones while driving. Oct 26-2:56 PM 6
Oct 27-11:38 AM Oct 27-11:26 AM 7
Name the undesirable methods used to obtain a sample from a population. Oct 26-4:55 PM Nov 7-10:17 AM 8
Oct 26-4:54 PM involves studying a part in order to gain information about the whole. Sampling Frame methods of sampling probability sampling simple random sampling (SRS) stratified random sampling cluster sampling systematic random sampling multistage sampling voluntary response convenience sample A sampling frame is the LIST of individuals from which a sample is selected. This list should include all of the intended population of interest. Apr 5-5:13 PM 9
Picking a Sample... Names out of a hat Label Random Rules Identify Oct 27-3:08 PM Oct 26-5:04 PM 10
Do different sizes of tickets example with class. Is this fair? Mar 12-11:13 AM Oct 31-12:19 PM 11
Mar 17-9:33 AM Nov 1-7:33 PM 12
Oct 31-12:11 PM Example on page 217 Label: Use 2 digit numbers start on line 131 and choose Identify sample: 00 71 66 32 81 41 48 73 78 55 76 45 19 59 65 65 68 73 05 Beach Castle 19 Sea Castle Oct 26-5:09 PM 13
Using Technology Seed Calculator first 323 Rand Identify Oct 26-5:11 PM Suppose that your are a regional manager in charge of all the WalMart stores in NYC that sells your company's LABEL: (N) STOPPING PROCEDURE: 084 214 475 377 377 287 447 559 208 563 791 409 245 453 645 668 126 142 147 836 126 091 537 398 481 145 926 Apr 5-5:16 PM 14
117 Rand Identify Oct 26-5:11 PM 117 Rand Identify Oct 26-5:11 PM 15
FINISH ACTIVITY Oct 26-5:17 PM Oct 27-4:01 PM 16
Using a random digit table to select random numbers. We must think of the numbers as three digits 001 to 150 Pick a random starting place... choose the sample of 5 words by "peeling off" three digits at a time. Only keep 3 digit numbers between 001 and 150, do not keep repeats. Mar 12-10:54 AM Oct 31-12:11 PM 17
Oct 28-3:05 PM Blocks 1, 2, and 4 Student Sample Random Sample Random Sample 2 3 4 5 6 7 8 Oct 27-3:19 PM 18
Type of sampling method? LABEL: Use 2 digit numbers from 01 30 to 30. 4 TABLE: Start on line 145 and choose 2 digit numbers. STOPPING PROCEDURE: Continue until 4 DIFFERENT 2 digit numbers between 01 and 30 are selected. IDENTIFY SAMPLE: 19 = Miranda 26 = Santos 06 = Elashoff 09 = Griswald LABEL: Use 1 digit numbers from 1 to 10 0 with 0 = 10. 2 TABLE: Start on line 123 and choose 1 digit numbers. STOPPING PROCEDURE: Continue until 2 DIFFERENT 1 digit numbers between 1 and 0 are selected. IDENTIFY SAMPLE: 5, 4 5 = Kim 4 = Gupta Apr 5-5:25 PM Put numbers on homework tables of names line 107 QUIZ ON CHAPTER 4 SECTION 2 NOTES TOMORROW Apr 6-9:53 AM 19
Use two digit numbers from 01 to 40 Start at line 107 choose two digit numbers. Continue until 5 DIFFERENT two digit numbers from 01 to 40 are selected 82 73 95 78 90 81 67 65 53 00 94 Sample consists of the following classmates. Johnson (20) Rider (31) Calloway (07) Oct 27-7:07 PM Use two digit numbers from 01 to 33 Start at line 117 choose two digit numbers. Continue until 3 DIFFERENT two digit numbers from 01 to 33 are selected 79 85 Sample consists of the following complexes Fairington (16) Fowler (18) Oct 27-7:09 PM 20
Oct 31-12:11 PM Use numbers from 1 to 1410 Seed Calculator with number 222 (just for classroom purposes) RANDOM: Use calculator command to generate random numbers RANDINT(1,1410,1) Continue until 141 DIFFERENT numbers from 1 to 1410 are selected Sample consists of the following plots. (do only first 3) Oct 27-7:09 PM 21
Use numbers from 1 to 55,914 Seed Calculator with number 555 (just for classroom purposes) RANDOM: Use calculator command to generate random numbers RANDINT(1,55914,1) Continue until 395 DIFFERENT numbers from 1 to 55914 are selected Sample consists of the following gravestones.(do only first 3) gravestones 43962, 1387, 4182 Oct 27-7:09 PM the theoretical probability of four 0 in 40 digits is exactly 4 but this will not always occur with a "random" sample of 40 digits. with 10 digits possible there is a 1/100 chance of two digits being 00 (or 100), this will not happen very often but there is a chance that four digits could be the number 0000. One out of 10,000 chance that it will occur. ALSO, this number 0000 is just as likely as any other 4 digits!! Think about it. Oct 27-7:10 PM 22
Picking the same "Random" sample each time will not result in your samples being "Random" any longer... Oct 27-7:10 PM To find the sample of 20 randomly selected phones might be a problem if you waited until the end of the day. Perhaps the managers could select 20 numbers from 1 to 1000 ahead of time. But then you would not want to tell the people manufacturing the phones which ones were selected for inspection... b) The last 20 phones are not a random sample so Bias could result. Perhaps the last 20 phones are of poorer quality than the first phones manufactured. Tired people or tired machines (over heated, etc.) could result in the ending phones not having the same quality. This is NOT a Simple Random Sample because all possible groups of 20 phones would not be equally likely to be selected. It would be impossible (probability = 0) for the 20 phones in a row to be selected. Perhaps 20 phones in a row might be a desirable group occasionally. Oct 27-7:10 PM 23
It would take a very long time (and time is money) to count and label all of the trees in the Rocky Mountain National Park. An SRS is not a pratical way to sample in this setting. sample could result in a bias sample. Perhaps the car emissions are contributing to the trees dying and would produce a result that overestimates the dead trees. c) Scientists should not conclude that exactly 35% of all pine trees on the west side of the park are infested because the sample yielded 35%. If the sampling method was carried out correctly they should have confidence that the approximate tree infestation is 35%. Sampling variability is the concept that each time a sample is selected it could result in different estimates of the true population "answer". These estimates should only slightly vary with proper sampling techniques. Oct 27-7:10 PM Mar 17-10:47 AM 24