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Chapter 18: TheChi-SquareProbabilityDistribution 279 Using Excel's CHIINV Function You don't have a chi-square distribution table handy? No need to panic. We can gen- erate critical chi-square scores using Excel's CHIINV function, which has the follow- ing characteristics: CHIINV(probability, deg-freedom) where: probability = the level of significance, deg-freedom = the number of degrees of freedom For instance, Figure 18.2 shows the CHIINV function being used to determine the critical chi-square score for = 0.10 and d.f. = 4 from our previous example. Figure 18.2 Excel's CHIINV function. Cell A1 contains the Excel formula =CHIINV(0.10, 4) with the result being 7.779. This probability is underlined in the previous table. Characteristics of a Chi-Square Distribution We can see from Figure 18.2 that the chi-square distribution is not symmetrical but rather has a positive skew. The shape of the distribution will change with the number of degrees of freedom as shown in Figure 18.3. As the number of degrees of freedom increases, the shape of the chi-square distribu- tion becomes more symmetrical.