Troubleshooting
Problem
I'm running chi-square tests in the SPSS CROSSTABS procedure. The tests are labeled as being 2-sided. What does this mean? Are they one-tailed or two-tailed?
Resolving The Problem
A one-sided test or directional test is one in which the direction of departure from the null hypothesis has been specified in advance. This is only applicable in the case of a single degree of freedom test, since with more than one degree of freedom, there is more than just a single direction by which the results can depart from the null hypothesis. Thus all tests involving multiple degrees of freedom for an hypothesis are going to be two-sided or nondirectional.
If the distribution being used in the test is symmetric, then one-sided corresponds with one-tailed. However, with distributions such as chi-squares and Fs, which are not symmetric, the standard tests use only one tail, but are two-sided, or nondirectional. The chi-square distribution with 1 df is the same as the distribution of the square of a Z or standard normal distribution. The F distribution with 1 numerator df is the same as the distribution of the square of a t with the same denominator df. Compare the critical values in tables or that you get from SPSS to verify these relationships. They show that a one-tailed chi-square test gives the same results as a two-tailed Z-test, and that a one-tailed F test gives the same results as a two-tailed t test; all are two-sided or nondirectional
Related Information
Historical Number
58423
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Document Information
Modified date:
16 April 2020
UID
swg21475375