Chi-square procedures

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Send your summary documents (in pdf format if possible) to jhl2881 at
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Suggested problems from Chapter 14:
goodness of fit: 3, 4, 5 (this is an example of how biologists use 2x2 tables to do goodness of fit tests), 9 (simulation)
2-way tables: 13, 19, 20, 14, 16, 18, 12, 17, 22, 24, 32, 33, 34.



We're beginning our last new topic (since we already did linear regression inference once).

We will use two different types of chi-square procedures and three different names for the procedures.

First, if some higher power determined what the proportions of the sample should have been associated with different values of the categorical variable. . .
like what portion of your M&Ms should have been red, brown, green, etc., then you will use a Goodness of Fit test to compare your experience (the sample) with what the higher powers suggested. This is also the test we use when the higher power might suggest that the distribution should have been "fair" or equal across all the values.


If the sample itself is going to suggest a distribution, then we use the test on independence or the test of homogeneity. These two tests are performed the same way, we just have different inputs and hypotheses associated with the two forms.

When we have one sample from one population and want to know if characteristics are associated, like red hair and green eyes, we might use the test of indepenence.

If we have two populations, like smokers and non-smokers, and want to know if the two populations had the same propensity for speeding tickets, we could use a test of homogeneity with cleverly-selected data.

Methods will be discussed in class.

Have the printed draft of your assignment in class on Wednesday!