X2 (chi-squared or 'chi-square' - statisticians are not agreed) is a statistical test based on a comparison between a test statistic and a critical value from a chi-squared distribution. A chi-squared variable can be regarded as the sum of a number of squared independent normal variables, each with zero mean and unit variance. The number of such squared terms is the number of degrees of freedom of the x2 distribution. A chi-squared test can be used to test the null hypothesis that two or more population distributions do not differ. When comparing observed values with those expected under the null hypothesis, it is the sum of the ratio of the squared differences between observed (O) and expected (E) values to the expected value:
There are two well-known versions, the Pearson %2 test and the Mantel-Haenszel test. See Statistical Significance.
48 Choice Modelling Choice Modelling
A conjoint analysis procedure for estimating willingness to pay for services using a weighted set of attributes of the services in question.
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