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http://en.wikipedia.org/wiki/Chi-squared_distribution

where at the bottom of the page, chi-square = sum of something devided by variance.

However, here:

http://www.napce.org/documents/research-design-yount/23_chisq_4th.pdf [Broken]

where the chi-square formula is that the sum of the same thing devided by expectation value.

Which formula is right then?

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# Why does Chi-square formula have two different ones?

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