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The Cliff´s Delta statistic is an effect size measure that quantifies the amount of difference between two non-parametric variables beyond p-values interpretation. This measure can be understood as a useful complementary analysis for the corresponding hypothesis testing. During the last two decades the use of effect size measures has been strongly encouraged by methodologists and leading institutions of behavioral sciences. The aim of this contribution is to introduce the Cliff´s Delta Calculator software that performs such analysis and offers some interpretation tips. Differences and similarities with the parametric case are analysed and illustrated. The implementation of this free program is fully described and compared with other calculators. Alternative algorithmic approaches are mathematically analysed and a basic linear algebra proof of its equivalence is formally presented. Two worked examples in cognitive psychology are commented. A visual interpretation of Cliff´s Delta is suggested. Availability, installation and applications of the program are presented and discussed.

This study investigates why reasoning that involves negation is extremely difficult. We presented participants with reasoning problems containing sentences with negation of conjunctions and disjunctions in order to test predictions derived from the Mental Models Theory of human thought. According to this theory, reasoning consists of representing and comparing possibilities. Different sentential forms would require different cognitive demands. In particular, responses to a sentential negation task would be modulated by working memory load. This prediction would hold for correct responses but also for the general pattern of responses that includes incorrect responses when the task offers different response options. A within-subjects experimental design with selection paradigm was applied to test these predictions. Experimental comparisons and a complementary descriptive study yielded evidence consistent with the theory-driven predictions derived from the Mental Models Theory. The working memory load was critical for the modulation of correct responses and overall responses. We discussed alternative accounts, and suggested additional predictions for further evaluation of these phenomena.