Abstract
The Evidence-Based Practice approach is based on the use of scientific research in decision-making in an effort to produce the best possible services in clinical practice. The knowledge level about effect size statistics and meta-analysis studies may affect the decision soft professionals and jeopardize the quality of psychological interventions. This paper presents the result so fan on-line survey on the degree of knowledge of these topics among Spanish practitioner psychologists. The sample consisted of 77 participants (68.8% women and 31.2% men), with a mean age of 41.44 years (SD=9.42), with age range of 25-64 years. The results suggest that most of the psychologists survey eddid not have adequate knowledge about effect size index, meta-analysis studies, or methodological quality checklists. It is therefore necessary to improve the statistical education of practitioner psychologists, which might also contribute to their provement of professional practice.