| Hand in (All D&V
p 238ff. unless otherwise noted)
1,4,6,7,8, 9 You did parts a,b,c,d,e of these; now add f and hand them all in. 21 Quality Control Use a cluster sample, again, now using the Random number table (p. A-49) : Get the individuals like this: Let the cases be labeled 61, 62,....80. Use line 16, reading across, to first choose 3 cases from 61, 62,....80. Write down which cases are chosen. Then choose one bottle from each case like this. Consider them labeled from 1 to 12: For each case, take a sample of size 1 to decide which bottle from that case; keep reading the table where you left off. Write down which bottles were chosen. (I want everyone to start at line 16 so everyone will get the same sample and Fay can tell if you did it "right!") 11 Parent opinion I
p. 267 #41 Security
|
Read,
to discuss p. 267 #29 Home-
p. 239 #13 Wording
|
Optional |
Homework questions? Day 20 Circulate your random samples from Old Faithful data.
Sampling, continued:
Sources of Biasin
sampling: any systematic failure of a sample (or its method) to
represent its population. (E.g. sampling
frame excludes "different" part of population.) see
Day 20
HW #21: Are we running a risk if we take the same (place) bottle from each case? (Maybe. Environment effects? Deliberate "stacking" of bottles?)
Exam: shall we postpone till Monday?? (My email
as of posting this: 2 for postponing--voluntary response sample...)
Yes. Will have definitely
completed Part III, exam will cover Parts II and III.
Using Random Number Table to sample (p. A-49) Every digit, every sequence of digits, is equally likely to be "next" in any direction. see Day 20
= = =
= = = = = = = = = = = = = = = = = = = = = = =
D&V Ch13 Goal:
show cause-and-effect. Predictor-->Response
Observational Study: Observe
individuals; don't do anything to them;
do not influence the responses. Can indicate
strength of relationship, differences, but not cause and effect.
(Often not with samples, but with selected group(s).) Lurking variables?!?
(Fisher: Smokers smoke to soothe irritabilities that may cause
cancer.)
Retrospective:
gather data after the fact (observe that x% of men hospitalized
with heart disease were/are smokers)
Prospective:
choose individuals in advance. Measure them; or follow them as events
happen. (Framingham Heart Study: 5,209 (2,873
women and 2,336 men) healthy residents between 30 and 60 years of age.
Followed from 1948 to now. A second-generation cohort recruited 1971, Minority
group 1995 http://www.framingham.com/heart/)
Experiment: Impose
treatments
on individuals, to see how the treatment
influences the response.
Compare treatments' effects.
Do something to: "Experimental Units" =
"Subjects"
Treatment: A Specific experimental condition.
Factor: = Explanatory (Predictor) Variable we manipulate.
Levels: Specific
values of a factor that we set.
Response variable(s)
E.g. 2 headache medications, in combination?
A two-factor experiment, each with 3 levels. 9 possible treatments.
Factor A: Aspirin: levels None, 500 mg,
1000 mg
Factor B: Caffeine: levels None, 50 mg, 100 mg
Response variable: reported pain relief
| Aspirin | ||||
| None | 500 mg | 1000 mg | ||
| None | Treatment 1 | Treatment 2 | Treatment 3 | |
| Caffeine | 50 mg | Treatment 4 | Treatment 5 | Treatment 6 |
| 100 mg | Treatment 7 | Treatment 8 | Treatment 9 |
E.g. (Day 13, MRA-95-13 )Corn yield=
response variable. One Factor = Planting rate. 5 Levels=the
rates.
Start here Monday
Principles of designing a comparative experiment
(p. 243)
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