Final answer:
By the 1990s, psychotherapy research had shown evidence supporting the effectiveness of certain therapies. Key figures like Sackett, Rosenberg, and Rogers contributed to the development of evidence-based practice in the field of psychology and solidified the efficacy of therapeutic techniques like CBT and client-centered therapy.
Step-by-step explanation:
By the 1990s, psychotherapy research had shown C) Evidence supporting the effectiveness of certain therapies. This period marked a significant shift towards recognizing the empirical foundations of psychotherapeutic interventions. Studies during this era demonstrated that various forms of therapy, such as cognitive-behavioral therapy (CBT), psychodynamic psychotherapy, and client-centered therapy, could be effective for treating a range of psychological disorders.
Significant contributions from scholars like Sackett and Rosenberg on evidence-based medicine and the meta-analyses carried out by Butler et al. on cognitive-behavioral therapy provided strong evidence regarding the efficacy of certain therapeutic approaches. Furthermore, client-centered therapy, rooted in the work of Carl Rogers, continued to be influential, and research such as that by Shedler noted the effectiveness of psychodynamic psychotherapy.
Overall, the culmination of research by the 1990s supported the evidence-based practice in psychology, establishing a firmer scientific basis for specific therapeutic techniques and their appropriateness for certain psychological conditions.