Hand in MONDAY
Note: We are finished with SPSS for a
while. None required for the next few chapters
.Postpone the rest.
Read, to discuss
p. 158, 5.42, 43 lurking variables, causality.
Especially do the ones for Ch. 8; they're really not optional.
. .. Ch. 8
p.220, 8.38 3 over 21
p. 222, 8.46 Canada healthcare
p. 219, 8.37
internet Use table B (more practice)
p. 220, 8.37 seat belt use (bias)
* There are 376,740 different possible
samples of size 6 from a list of 28.
does not imply causation http://xkcd.com/552/
Establishing that x "causes" y:
Best: Do an experiment in which we change x, keep lurking variables under control. (E.g. Rats. More in Ch.9)
Otherwise: Strong association. Consistent over many studies. Higher x-->stronger y. X precedes y in time. A plausible mechanism exists (parallel studies?)
Chapters 1 through 5
have covered analyzing data that was given to us--what it said about itself.
Informally, develop guesses, suspicions, hypotheses about the world the data came from.
From Exploration to Inference p. 198
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.
.Your digits! .
Sample survey: (attempt to) choose a representative
sample from a large, varied population. Not Easy!
Some issues: What population do we want to understand? What exactly do we want to measure? (Pre-Election polls--pitfalls?) (2010 Census: Determines Congressional districts, and much else. Under Dept. of Commerce. Can we use sampling techniques? Not to determine Congressional Districts, but for other things. Counting/sampling issue background: 3 )
Non-probability samples (sampling badly):
Why the same number of digits in each label? Each individual 3-digit chunk is as likely as any other 3-digit chunk. But a 1- or 2-digit chunk is more likely than any 3-digit chunk. So 2 will come up more often than 12, but 02 will come up just as often as 12.
Why across? For consistency
on HW, go the way they say (so you get the answer in the book).
In practice, you can read up, down, backwards, as long as you decide
beforehand, and don't change in the middle of choosing the sample.
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