Final answer:
Healthcare professionals and community psychologists are responsible for ensuring that treatment is effective for culturally diverse clients by developing culturally tailored interventions and employing methods such as community-based participatory action research.
Step-by-step explanation:
Responsibility for ensuring treatment is effective for culturally diverse clients falls on healthcare professionals who are expected to deliver culturally competent care. This includes understanding and integrating the cultural, social, and linguistic needs of patients into treatment plans to enhance their effectiveness. Healthcare providers, along with community psychologists, work together to develop and implement culturally tailored interventions to address the unique needs of varied populations. Ensuring effectiveness in treatment requires methods like community-based participatory action research (CPAR) and utilizing mixed-method approaches to provide context to quantitative data, thus helping in overcoming health disparities and improving health outcomes.