Solved – Use CHIINV or CHISQ.INV to report Chi Square statistic

chi-squared-testexcel

I'm looking to report a chi-squared statistic for a chi-squared goodness of fit test using a 2×2 table.

....Treatment 1.... Treatment 2
Yes 100 120
No 30 50

I'm looking to see if the proportion of Yes/No differs between the two treatments (equal=null, different=alternative hypothesis).

A chi-squared test is easily done by computing the expected values in excel, and using the CHITEST function to compute the p-value. However, I also need to report the chi-squared statistic itself, not just its associated p-value.

According to Microsoft, CHISQ.INV Returns the inverse of the left-tailed probability of the chi-squared distribution, while CHIINV returns the inverse of the right-tailed probability of the chi-squared distribution.

If I'm looking to report the chi-squared statistic for a chi-squared test (e.g. in APA format), which one should I use? Is there another way to have Excel report the chi-squared statistic for a 2×2 table?

Thanks

Best Answer

The p-value for that chi-square you're doing is the area in the right tail beyond the test statistic.

Help for CHIINV says:

CHIINV(p, df) is the inverse function for CHIDIST(x, df). For any particular x, CHIDIST(x, df) returns the probability that a Chi-Square-distributed random variable with df degrees of freedom is greater than or equal to x.

So that's what you need.

As a check, compute the statistic by hand for an example you already know the statistic for (or one you make up; in either case with large enough expecteds that the chisquare approximation will be fine), and check that the p-value generated for that (using something that calculates a p-value for a chisquare) inverts to give the statistic you had or calculated (or very close to it)

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