Determining the Best Research Design for Meditation Study

In psychological research, understanding the intricacies of research methods is fundamental to establishing valid findings. Consider a scenario where a psychologist is interested in examining the long-term effects of daily meditation on stress levels. To ensure that their research produces reliable and valid results, the psychologist must choose a study design that adequately controls for potential confounding variables, such as prior mental health issues, current stressors, and participants' lifestyle habits. Which of the following research designs would best enable the psychologist to draw causal conclusions about the effects of meditation on stress?