|
Hand in Ch.
8,
cont. p. 227, 9.4, 9.5, 9.6 treatments, factors,
response, etc. Can do now: Hand
in
Monday after Break, Day 24 Separate
paper: |
Read, to discuss p.220, 8.38 3 over 21 p. 221, 8.43 guns p. 214, 8.13, 8.14 biases. p. 222, 8.44 wording survey questions p. 222, 8.46 Canada healthcare p.210, 8.10 Sampling pentacostals (size) = = = = = = |
Optional p. 219, 8.37 internet Use table B (more practice) p. 220, 8.37 seat belt use (bias) |
Exam 2 handed
back.
Link to statistics,
comments, solutions. I may make a
few more comments on content on Wednesday
Midterm grades will be posted by Friday afternoon; will be slanted
pessimistically at the high end.
Because it's so important to have control of the Normal
distribution:
Makeup
work to get 90% of the 42 Normal distribution
points. To me
by 3:30
pm Day 27 (Monday, April 2--2 school weeks). START
NOW! (Print
the sheet if you need it.)
=
= =
= = = = = = = = = = = =
= = = = = = = = = = = = = = = =
On the sign-in clipboard. Next to your
name:
Put the number of East Asian surname individuals in your
SRS,
(p. 209 8.7) Be sure it's in your HW also, with the
names of your
sample! If you did it
with another person, put that on the clipboard!
recap: Ch. 8&9: Producing Data: Aim:
create data sets that will allow us to make inferences to
a
larger world than just the data we have.
(SAMPLING) BIAS: The design of a study is biased
if
it systematically favors certain outcomes.
Non-probability samples (sampling badly): Voluntary
response sample , Convenience
sample
Our main sampling design:
Simple Random Sample (SRS) of size n: n
individuals chosen in such a way that every
possible set of n individuals
has an equal
chance of being chosen.
Homework Questions Day
20
New today:
Using Random Number
Table.
See Day 20 for details.
(Simple
Random Sample Applet, done last time. Enter population
size,
sample size, hit Reset, then Sample.)
See Day 20 for rest of details on Ch. 8:
Some more sources of bias:
**Undercoverage: One possible source
of
undercoverage: your Sampling frame excludes some
individuals.
** Nonresponse
**Response bias
**Wording of questions
A random sample (p.210) is from a design where
impersonal chance is used to pick the individuals. SRS (p.
205)
is the
most straightforward. More sophisticated methods are often
used,
but they're optional this term. (More
info)
+ + + + + + + +
Larger (RANDOM) samples give more accurate results than smaller
random samples.
(but Not because you have more of the population.)
More discussion of terms used
in
sampling
.Start Ch.
9 Wednesday.....
= = = = = = = = = = = = = = = = = = = = = =
Chapter 9, intro
Observational Study: Observes individuals, measures
variables, does not influence the responses. (ch.8)
Sometimes
observe individuals who are (more or less) conveniently at
hand, or, better,
Take
Sample from a population, examine it.... (ch.8)
Experiment: Imposes treatment
on individuals, to see how the treatment influences
the
response. (ch.9) Confounding:
Two variables (explanatory or lurking) are confounded
when
you can't sort out their effects on a response variable.
(Rats: Mothers' grooming causes sociability, or inherited
sociability from mothers who like to groom? Health: Coffee and
cigarettes (till recently)).
Designing Experiments
Different
jargon; different traditions.
Do something to:
"Experimental Units" = "Subjects"
= individuals.
Treatment: Specific experimental condition we
impose
on one or more subjects.
Factor: Explanatory Variable we
manipulate.
There will be Specific values of a
factor that
we set.
(Sometimes called "levels")
Response variable(s) Results that we measure.
E.g. Corn planting
(HW
day ??, p. 116, 4.32) 1
factor = planting rate. 5 different values (levels). 16
individuals (plots of ground). Response: yield per acre.
E.g. 2 headache medications, in combination?
A two-factor experiment, each with 3 values (levels).
9
possible treatments.
Factor A: Aspirin: values: None, 500 mg,
1000 mg
Factor B: Caffeine: values: 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 |
| Sievers home | Math151-Sp12/Days21.htm | 1pm | 3/12/12 |