Experimental design is a research methodology used in various scientific disciplines to carefully plan and conduct experiments in order to gather valid and reliable data. It involves systematically manipulating variables to investigate cause-and-effect relationships, controlling for potential confounding factors, and ensuring that results are both internally and externally valid. Experimental design typically includes steps such as selecting a sample, random assignment of participants to different experimental conditions, and replicating the experiment to ensure the reliability of findings. This approach allows researchers to test hypotheses and draw conclusions about the effects of specific variables on the outcome of interest.