Math 143 C/E, Spring 2001
IPS Reading Questions
Chapter 9, Section 1 (up to ``Beyond the basics", p. 632)
- How is this material on inference for 2-way tables
related to and an extension of the 2-proportion
inference procedures we learned in Section 8.2?
- Just like when we used the normal approximation to
a binomial distribution, the chi-square distribution
is only approximately accurate and should be used
with attention paid to whether it will give a close
approximation in a given setting. What does the text
say are ``safe" situations (ones where the chi-square
test should be relatively accurate)?
- In what sense should a certain count in a cell
be expected? To date, I have provided no
justification for the term ``expected count", let
alone a reason behind the formula. Try this exercise,
forgetting any formula that you know. Below is a 2-way
table where all of the individual cells have been left
blank. The only information you have are the marginal
distributions. Operating under the assumption that
the two populations (columns) are no different (that is,
that they have the same conditional distributions), try
to fill in the counts for each cell. (Note: the totals
should work out for both columns and rows.)
| Gender | | |
Smoking Status | Female | Male | Total |
Non-smoker | | | 261 |
Smoker | | | 37 |
Total | 175 | 123 | |