01a ch12 handout and notes

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					Sampling Design Notes                         Types of Sampling Designs:
                                              Simple Random Sample (SRS)
How do we gather data?

1) population -                               Stratified random sample

2) census -

3) sample –                                   Systematic random sample

4) sampling design –

                                              Cluster sample
5) sampling frame –

6) random digit table –

                                              Multistage sample

7) bias –

Why would we not use a census all the time?
Identify the sampling design:                             Sources of bias in Surveys:

1) The Educational Testing Service (ETS) needed a
sample of colleges. ETS first divided all colleges into
groups of similar types (small public, small private,
etc.) Then they randomly selected 3 colleges from
each group.

2) A county commissioner wants to survey people in
her district to determine their opinions on a
particular law up for adoption. She decides to
randomly select blocks in her district and then survey
all who live on those blocks.

3) A local restaurant manager wants to survey
customers about the service they receive. Each night
the manager randomly chooses a number between 1 &
10. He then gives a survey to that customer, and to
every 10th customer after them, to fill it out before
they leave.

                                                          What is the source of bias?
Random Digit Activity                                     1) Before the presidential election of 1936, FDR
Suppose your population consisted of these 20             against Republican ALF Landon, the magazine Literary
people:                                                   Digest predicting Landon winning the election in a 3-
                                                          to-2 victory in a survey of 10 million people. George
 1)    Aidan             11) Kathy                        Gallup surveyed only 50,000 people and predicted
 2)    Bob               12) Lou                          that Roosevelt would win. The Digest’s survey came
 3)    Chico             13) Matthew                      from magazine subscribers, car owners, telephone
 4)    Doug              14) Nan                          directories, etc.
 5)    Edward            15) Opus
 6)    Fred              16) Paul
 7)    Gloria            17) Shawnie
 8)    Hannah            18) Tracy
 9)    Israel            19) Uncle Sam                    2) Suppose that you want to estimate the total
 10)   Jung              20) Vernon                       amount of money spent by students on textbooks
                                                          each semester at SMU. You collect register receipts
                                                          for students as they leave the bookstore during lunch
Use the following random digits to select a sample of     one day.
five from these people.

 1 4 5 1 8 0 5 1 3 7 1                                    3) To find the average value of a home in Plano, one
 2 0 1 5 5 8 0 1 5 7 0                                    averages the price of homes that are listed for sale
 3 8 9 9 3 4 3 5 0 6 3                                    with a realtor.
                        HOW GOOD IS A CENSUS?

         A FAIRY TALE

     While strolling through a glen, a giddy English girl tripped
on a rather large, almost gigantic frog. The girl staggered but
regained her footing and was about to go on when the frog
began to speak and gesticulate to gain the girl's attention. "I
have not always been a frog," he croaked. The frog's green
coloring seemed to glow brightly as he continued. "I was once a
gracious knight. A gentleman called Gallant George Grenville,
but was changed into this ghastly frog you now see by an
ungodly, magical genie. The spell can only be broken if I gain a
girl's good graces and spend a night in her garden." The agog
girl was skeptical, of course. She gazed at the frog's pleading
eyes and soon her doubts gave way to her giddy nature. Giggling,
she decided to grant the frog's wish and took him home
straightway, putting him by her garden gate. That night the girl
slept grandly and sure enough, when she awoke the following
morning, there alongside her garden gate was the gracious
knight, George Grenville. Well, strangely enough, for a long, long
time the girl's mother did not believe that story.

Total: ________
The Jelly Blubber Sampling Design Activity
Judgmental Sample –      Select 5 Jelly Blubbers that, in your judgment, are representative of
                         the population on this sheet. Record the lengths of your five Blubbers
                         and find the mean.

      _______      _______      _______      _______      _______             x = _______

Simple Random Sample - Find five random numbers between 1 & 100. Locate the corresponding
                       Jelly Blubbers and record their lengths. Find the mean.

      _______      _______      _______      _______      _______             x = _______

Stratified Sample -      Suppose one shakes the Jelly Blubbers, causing the larger ones to sink
                         and the smaller ones to rise. The result is the sheet of stratified
                         Blubbers, where the sizes are divided into 5 strata. Choose one
                         Blubber at random from each stratum by choosing a random number.
                         Locate the Blubbers & record their lengths. Find the mean.

      _______      _______      _______      _______      _______             x = _______

Systematic Sample -      A system is used to select the sample. Use the original page of
                         Blubbers and select five Blubbers. Choose a random number between
                         1 &20. This is the first Blubber. Then add 20 to each previous
                         number to find the other four Blubbers. Record their lengths and
                         find the mean.

      _______      _______      _______      _______      _______             x = _______

Cluster Sample -   Cluster samples select whole groups or clusters of individuals (usually based
                   on location). Choose a random number (r) between 1 & 20 and multiply by 5.
                   Your sample will be that number (5r) and the four numbers preceding it.
                   (Example: r = 12, 5r = 60, so sample is 60, 59, 58, 57, 56) Record the
                   lengths of the Blubbers and find the mean.

     _______       _______     _______      _______      _______             x = _______

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