Experimental studies that manipulate treatment procedures to investigate their direct effects on treatment processes and outcomes are necessary to find out the effective elements and improve the effects of cognitive behavioral therapy (CBT) for depression. The present study randomized mildly to severely depressed participants into a procedure focused on cognitive therapy skill acquisition (CTSA; n = 27) or a control procedure focused on being exposed to theories of automatic thinking (n = 25) and investigated the direct effects on cognitive therapy (CT) skill use, credibility of idiosyncratic dysfunctional beliefs and strength of emotions. After the procedure, participants were exposed to a sad mood induction and given an assignment to test their CT skills. Participants who received the CTSA procedure used more CT skills compared to participants that received the control procedure, but there were no differences between conditions in the decrease of the credibility of idiosyncratic dysfunctional beliefs and strength of emotions. However, in participants with mild levels of depression, those who underwent the CTSA procedure showed larger decrease in the credibility of their most malleable belief (i.e. mostly automatic negative thoughts) compared to those who received the control procedure, but the significance of these findings disappeared when controlling for differences in ratings of the procedures. Future experimental studies should focus on the effects of CT skill training in the long term, the dose of the procedure and individual patient differences to find out under what circumstances the use of CT skills can lead to a reduction in dysfunctional thinking and subsequent symptoms of depression.
Keywords: CBT; Cognitive therapy skill acquisition; Cognitive therapy skills; Depression; Dysfunctional thinking; Experiment.
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