Self-rated high did not significantly correlate with age, education, amount of cocaine used over the last 6 months, years of cocaine use, days since last use of cocaine, craving for cocaine, or general psychiatric symptoms on the day of cocaine administration or during the 30 days before admission (p>0.14). The correlation between area under the curve for high and Beck Depression Inventory scores on the day of infusion was significant (r=0.56, df=15, p=0.02). Because craving for cocaine and Beck depression scores on the day of cocaine administration correlated significantly (r=0.72, df=15, p=0.003), a partial correlation controlling for craving was employed. This did not affect the significant correlation between Beck depression scores and area under the curve for high (r=0.64, df=12, p=0.01).
Subsequent analyses revealed that on the day of cocaine administration, seven of the 17 participants reported clinically significant levels of depressive symptoms (i.e., Beck depression score of 11 or more) (14). To identify the symptoms that differentiated between the groups, a gamma statistic was employed (15). Gamma provides a method for examining the relationship among ordinal variables, such as Beck Depression Inventory responses. Because gamma was calculated for each of the 20 items on the Beck Depression Inventory, a family-wise correction set alpha at 0.01 (16).
Participants with higher Beck depression scores were more likely to respond positively to the following items: feelings of failure (gamma=–0.97, df=15, p<0.001), anhedonia (gamma=–0.96, df=15, p<0.001), feelings of guilt (gamma=–0.92, df=15, p<0.001), self-hatred (gamma=–1.00, df=15, p<0.001), self-blame (gamma=–1.00, df=15, p<0.001), indecisiveness (gamma=–1.00, df=15, p<0.001), motivation (gamma=–1.00, df=15, p=0.003), and fatigue (gamma=–1.00, df=15, p=0.003). Participants with higher Beck depression scores were not more likely to report sadness, discouragement, tearfulness, suicidality, or other symptoms of syndromal depression (p>0.05).