Table of Contents
1. Week 1 Lab
1.1. Starsign
Does your star sign have an effect on whether you believe astrology is scientific??
1.2. Measures of association
We have discussed the following measures of association, defined for 2*2 tables:
- Difference in proportions
- Relative rate or ratio of proportions
- Odds ratio
Calculate each of these measures for the following table:
| Outcome | |||
|---|---|---|---|
| No | Yes | Total | |
| Type 1 | 380 | 120 | 500 |
| Type 2 | 420 | 80 | 500 |
| Total | 800 | 200 | 1000 |
1.2.1. With a spreadsheet…
This spreadsheet will allow you to explore these measures a bit more. You can change the numbers in the "Type 1/Outcome Yes" and "Total/Outcome Yes" cells and the three measures are calculated for you. Use it to check what you have calculated by hand.
For "Total/Outcome Yes" values of 100, 200, 400, 800 and 900, do the following:
- Find what values of "Type 1/Yes" give you a difference in
proportions of 0.2 for each of these totals
- Find what values of "Type 1/Yes" give you a relative rate of 2.0
(or as close as possible) for each total
- Find what values of "Type 1/Yes" give you odds ratio of 2.0
(or as close as possible) for each total
Keep a note of your numbers and compare their patterns. What do you notice?
1.3. Adding capabilities to Stata
Lots of people write additional procedures for Stata, and many of
these are easily available. See help net and help
ssc for an overview. We are going to use one such add-on,
TAB_CHI, today. Do net search tab_chi first,
just to see how to search. One place it is found is the Stata web site,
and another is the Repec economics article archive. Either of the two
following commands should install it:
net install tab_chi
or
ssc install tab_chi
The former looks on the Stata website, the latter on the Statistical Software Components archive.
Once it is installed, load the NLSW88 data and try the following:
sysuse nlsw88, clear tabchi occupation union tabchi occupation union, noe noo adj