Final answer:
Random assignment allows for the control of confounding variables in an experiment, making it possible to establish cause-and-effect relationships between the independent and dependent variables. This method ensures that lurking variables are equally distributed and the experiment is controlled and unbiased.
Step-by-step explanation:
Random assignment is what allows researchers to draw cause-effect conclusions in an experiment through the control of confounding variables. This process is critical in experimental design, ensuring that any other variables that could affect the outcome (referred to as lurking variables) are evenly distributed across both experimental and control groups. This means that any observed differences between these groups after the experiment can be attributed to the manipulation of the independent variable.
Moreover, during an experiment, the independent variable is deliberately changed by the researcher, while the dependent variable is what is measured and statistically analyzed. By maintaining this control, the researcher can study whether changes in the independent variable cause changes in the dependent variable.
A control group receiving a placebo is one way to guard against expectancy biases that might otherwise influence the results. When the experiment is double-blind, both the researchers and the participants are unaware of group assignments, further reducing any potential biases. In conclusion, it is the rigorous application of random assignment that allows for a controlled experiment and the possibility of establishing a cause-and-effect relationship.