ABSTRACT
This chapter argues that a chi-square test reveals if there is a statistically significant difference between the frequencies of a variable across different groups. Like with ANOVA, tests have to be run to determine the relative rankings of the group frequencies. Thus, the chi-square test is run first, and if the result is significant, then post hoc tests are run as a follow up to determine which group differences are significant and the relative ranking of the group frequencies. The severe combined immunodeficiency (SCID-I) was used to determine the presence of obsessive-compulsive disorder (OCD). Tic disorders were also diagnosed according to diagnostic and statistical manual of mental disorder (DSM-IV) criteria. Chronic Tic Disorder (CTD) was diagnosed when a patient had either vocal or motor tics. Tourette Syndrome (TS) was diagnosed when a patient had both motor and vocal tics at some point. Post hoc analyses were performed with the Chi-square tests for the categorical variables with the Bonferroni correction.
