chi-squared

# chi-squared - BICD100 Genetics W08" Chisholm The...

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The chi-squared test for goodness of ﬁt. This is the “basic” chi-squared test. To test how well observed data ﬁt expected data for some number of classes (3:1, 1:1, 9:3:3:1, etc). The classes are assumed to be independent: e.g. being round yellow does not affect the probability of another pea being round green. The null hypothesis gives us the expected numbers (based on other hypotheses of independent segregation, dominance, etc, but we are not testing these explicitly--we are just testing the ratio.) Degrees of freedom: As the total is deﬁned, if there are n classes only n-1 can vary independently. So the degrees of freedom is always 1 less than number of classes. The chi-squared test for independence This is slightly different from chi-squared test of goodness of ﬁt. Here we test the null hypothesis that two probabilities are independent. For example if A and B are unlinked then the probability of being A should be independent of the probability of being B or b.

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## This note was uploaded on 06/07/2008 for the course BICD 100 taught by Professor Nehring during the Winter '08 term at UCSD.

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chi-squared - BICD100 Genetics W08" Chisholm The...

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