| Hand
in Monday(?) Chapter 13 p257ff. 21 Mozart do b 26 Swimming do d (be clear about what state re depression your subjects should be in to start with) 33 Beetles (+ make diagram ) 32 a, b, c Shingles On the separate page and keep it: 1,2,4,5,6,10,11,12,17,18 . Work on the experiment ones now: Do b,c,d,e, g, h, and see if you can pick out which ones are completely randomized (part of f) We'll finish them when we look at the other designs. - - - - - - - - - - Postpone: Other designs: 1,2,4,5,6,10,11,12, 17, 18 Finish these for those that are experiments . 32 d Shingles, "better" design 35 Safety switch 36 Washing clothes From Review part III, p. 263ff. 26 Laundry 34 Pubs |
Read,
to discuss
Review Part III: |
Optional |
Fay's hours:
Fay writes: " An emergency has come up and I will have to reschedule
myWednesday hours. I will be here from 1 (maybe 1.30) until 3." [SRS
says: I can work with you 12:30 on]
Fay's Review Session - a reminder. "There will be a session on Thursday
night at 7pm in the Math Clinic. Make sure to go through the practice
exam and bring questions."
Homework questions? Day 22
General exam questions?
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D&V Ch13 Goal:
show cause-and-effect. Predictor-->Response
Observational study/experiment, Intro
to Experiment, Day 22
Experiment:
"Experimental Units" =
"Subjects"
, Treatment, Factor: Levels
Response variable(s)
Principles of designing a comparative
experiment
(p. 243) Control,
Randomize, Replicate:
(Block--shortly )
Results: Measure differences in the response variable
for different treatments (e.g. side by side boxplots)
Completely randomized: all
experimental
units allocated at random among the treatments.
Diagrams p. 248: show sequence: random allocation,
groups:
counts and labeled treatments, compare results.
E.g. does acupuncture work for PMS? Response:
report of symptoms.
One factor, 3 Levels: None (music?),
Acupuncture
(wrong places), Acupuncture (right places). 3 treatments.
30 subjects with PMS:
Randomize,
10 each treatment. Administer treatments. Compare symptoms.
(Do diagram)
Picking groups with random number table: Pick "sample"
of size 10 from the 30 for first treatment. Pick another "sample"
of size 10 for 2nd treatment, from the remainder. The 10
remaining
get the 3rd treatment.
(Equal numbers to each treatment group is usually desirable,
or roughly equal....)
Bias: issues,
how to avoid...
--Subjects are not (usually) a random sample from the population;
generalize
with care. (Most psychology "facts" were based on studies of
Ivy
League males, before 1970's.) But random assignment to
treatment
groups should "equalize" some biases, differences cancel out.
--"Control" treatment is done to "control" group: baseline
or zero-level treatment to compare to. (Contrast with
"control"
of extraneous sources of variation.
)
--Blinding participants to treatment to prevent prejudgments,
expectations, subtle changes. Don't know which treatment.
+Those who can influence results
(subjects,
treatment administrators, technicians, nurses, etc.)
+Those who evaluate results
(judges,
physicans, etc.)
Single blind: everyone in one
category.
Double blind: everyone in both categories. (Drug:
bottle
labeled by number. Which is which is not revealed till the
results are
in.)
--Placebo effect: a real improvement in symptoms and/or
disease, resulting from a treatment that "should" have no medicinal
effect.
Placebo
("I
shall please") mimicking real treatment is used as control.
--Confounded variables (p.253): are usually either experiment
factors, or one(s) we didn't think about or control for
(lurking).
If the levels of two variables "travel together" (so we can't sort out
which one an effect is due to) they are "confounded".
Usually an experiment treats the placebo effect as a
potentially
confounding
variable, and is designed so placebo effect will work
equally
on all groups. There is no attempt to measure
the
placebo effect. ("All" drug studies.)
PMS/acupuncture:
Acupuncture (wrong) vs. Acupuncture (right).
&& Sometimes an experiment deliberately tries to measure
the placebo effect (as in the articles).
Acupuncture (wrong) vs.
Music.
Start here Monday
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Good practice: Beware confounding;
record everything you
can in case it turns out to be important; do pilot experiment.
Matched pairs is a special case of block design--each pair is a
little
"block":
Matched pairs: In experiment, to
compare Control and experimental
treatments
(i.e. 2 levels)
Sort experimental units into "matching"
pairs.
One member of pair gets control, other gets experimental.
Randomize which.
Compare within pair (find
difference),
then summarize all comparisons.
Common: Do the control and experiment to same
individual (matched with self). (Randomize which is first,
L/R...)
Eliminates extraneous variability.
Are right feet bigger than
left feet? (not an experiment) Sunburn
salve
experiment?
Matching is also often used in observational studies: try to
match individuals differing only on the potential cause-effect
variables,
so confounding variables will "subtract away".
&&I don't like the way the answer book diagrams Matched
pairs. Inconsistent with rest.
"Two-factor" (p. 252) vs. "one-factor with blocking" (p.251)
&&
A factor is a variable the experimenter can and does
manipulate (aspirin dose level); experimental units get assigned factor
levels using randomization.
A blocking variable is one whose values "come
with"
the experimental units and can't be changed by the experimenter (M/F,
smoker/nonsmoker,
age). The experimenter can require that a certain number of
individuals
have the blocking variable values desired ("30 M and 30 F were
recruited")
but can't impose those characteristics on the individuals. (Can't say
"You
will be M and you will be F")
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