How to ensure the randomness of samples in experimental design?

Ensuring sample randomness requires deliberate application of randomization techniques to assign participants to experimental groups solely by chance, preventing selection bias. This is achievable through structured procedures. Key principles include using unpredictable assignment mechanisms for every experimental unit and maintaining allocation concealment until assignment occurs. Necessary conditions involve a defined sampling frame and employing verifiable randomization methods, such as computer-generated random number sequences or published random number tables. Applicability spans controlled trials and observational studies where group comparability is essential. Crucially, the process must be free from researcher or participant influence on assignment order to maintain validity. Practical implementation involves these sequential steps: first, defining the eligible population and sampling units; second, selecting an appropriate randomization method matching the design (e.g., simple, block, or stratified randomization); third, generating a fixed, concealed allocation sequence using a reliable tool; and fourth, strictly adhering to this sequence during participant enrollment and assignment without deviations. This rigorous process enhances internal validity by producing comparable groups, enabling unbiased estimation of treatment effects and strengthening causal inference.