"A Million Random Digits book"
Your Graph experiment data? Better
at pies or bars?? Slower? (My graph data). More than
one appropriate analysis to understand the results.
Control: Warmup to cut down "practice" effects.
Colors the same. Others?
Randomize: Which came next, what sizes.
Replicate: Many of each type.
Continuing Design of Experiments:
HW questions?
Will begin here Monday:
Placebo effect article:
a) Give two examples of the placebo effect
b) What do researchers believe causes the placebo effect?
Usually an experiment treats the placebo effect as a 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 article).
Acupuncture (wrong) vs.
Music.
Principles of designing an experiment (p. 143/ACT 11-1)
Your Graph experiment data? Better
at pies or bars?? Slower? (My graph data). More than
one appropriate analysis to understand the results.
Control: Warmup to cut down "practice" effects.
Colors the same. Others?
Randomize: Which came next, what sizes.
Replicate: Many of each type.
Lack of realism Do sociology, psychology experiments generalize to "real life?" (Most psychology "facts" were based on studies of Ivy League males, before 1970's.) Ethical questions...
Statistical Significance
p.194: An observed effect so large that it would rarely occur by chance
(assuming no real difference in treatments) is called "statistically significant".
"So large", "rarely", "by chance" will be defined and quantified in
Ch. 6.
Example: Suppose 95% of the subjects
had their headaches cured by treatment 9 and only 25% by treatment
1 (placebo). IF the medicine in fact did "no good" that would be
a very unlikely outcome. So we will say the difference in headache
cures between treatment 1 and treatment 9 is "statistically significant"
and be inclined to believe the medicine "works".
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Fancier designs (not "completely randomized") Control extraneous
variability by presorting individuals into homogeneous groups.
Matched pairs: 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,
then
summarize all comparisons.
Common: Do the control and experiment to same
individual (matched with self). (Randomize order)
Are right feet bigger than
left feet? Sunburn salve?
Aside: Sampling data, "longitudinal study"
following same people through time.
Works like matched pair to control variability.
Block design: Sort experimental units into "Blocks"
= groups homogeneous on potentially confounding variables
e.g. M/F, age, income, weight, fruitflies
wild or curly-winged.
Within each block, randomize the treatments.
Compare
results within each block, then summarize all results.
(Matched pairs is a special case of block design--each
pair is a "block".)
Florence Nightingale, if time permits. (http://www.math.yorku.ca/SCS/Gallery/flo.html
, rustic
link)
| Read Moore, P.210.Exploratory Data Analysis vs. Statistical Inference
(If you plan to be absent Monday, please do the following anyway, email me the results if possible.) Do p. 216, 4.4 spinning penny Spin a penny 50 times, keeping track of Heads or Tails. Bring to class # of heads , #of spins, proportion that came up heads (# of heads divided by # of spins) A. Do this: Use the random number table in your book to pick 25 digits from 0,1,2,3,4,5,6,7,8,9. Do it like this: decide on a direction, up, down, across. Then close your eyes and put your fingertip (or pencil tip) blindly into the random number table. Open your eyes and start going from that point in your chosen direction till you've gone through 25 digits. Tally them as we did in class with the digits you "picked". Bring tally to class. 0| 1| 2| 3| 4| 5| 6| 7| 8| 9| |
HW assignment Day 21, Friday March 15,
Moore, from The Basic Practice of Statistics
Reading: ReRead section 3.2, Read Significance, Matched pairs
and block design; review ch. 3.
Next: We'll do p. 210, then 4.1, 2, 3.
Skip 4.4 and Skip Ch. 5.
| Hand in: Will all be part
of Day 22 assignment:
p. 199 3.43 hand strength 3.45 weight loss 3.44 student traders. The difference in the treatments is whether or not they have software that can make "charts" of past "trends." (If they don't have the software they don't have "charts") = = = = = = = = = = = = = = = = Significance p. 195 3.40 |
Read, to discuss
Matched pairs and blocks p. 209 3.72 McDonald's vs Wendy's p. 209 3.71speeding the mail
|
Optional
(more of same) p. 203, 3.58 3.59
|
| Sievers home | Math151-Sp02/Day21.htm | 1pm | 3/24/02 |