# Segment 33. Contingency Table Protocols and Exact Fisher Test

#### Watch this segment

(Don't worry, what you see statically below is not the beginning of the segment. Press the play button to start at the beginning.)

{{#widget:Iframe |url=http://www.youtube.com/v/9Qrkw5UfAmQ&hd=1 |width=800 |height=625 |border=0 }}

The direct YouTube link is http://youtu.be/9Qrkw5UfAmQ

Links to the slides: PDF file or PowerPoint file

### Problems

#### To Calculate

1. How many distinct m by n contingency tables are there that have exactly N total events?

2. For every distinct 2 by 2 contingency table containing exactly 14 elements, compute its chi-square statistic, and also its Wald statistic. Display your results as a scatter plot of one statistic versus the other.

#### To Think About

1. Suppose you want to find out of living under power lines causes cancer. Describe in detail how you would do this (1) as a case/control study, (2) as a longitudinal study, (3) as a snapshot study. Can you think of a way to do it as a study with all the marginals fixed (protocol 4)?

2. For an m by n contingency table, can you think of a systematic way to code "the loop over all possible contingency tables with the same marginals" in slide 8?