How to ensure the intrinsic validity in experimental design?

Internal validity refers to the extent an experiment establishes a reliable causal relationship between an independent variable (IV) and a dependent variable (DV), indicating the observed effect is likely caused by the manipulated IV and not confounding factors. Essential principles include utilizing robust randomization techniques for participant assignment to groups, thereby minimizing selection bias and pre-test differences. Strictly defining and operationalizing variables ensures accurate measurement. Actively identifying and implementing controls for potential confounding variables or extraneous factors is critical. Ensuring consistent application of experimental procedures across groups reduces unintended variability. Careful planning is also required to counter validity threats like maturation, history, testing effects, or instrumentation drift through appropriate design choices like control groups and blinding. Ensure intrinsic validity through specific methodological steps: 1) Implement true random assignment of participants to treatment and control groups. 2) Include an adequately sized control/comparison group receiving no treatment or an alternative. 3) Use blinding procedures (single or double-blind) to minimize participant and experimenter bias. 4) Precisely define and reliably measure the DV and consistently manipulate the IV. 5) Identify key covariates and potential confounders beforehand, incorporating them statistically via ANCOVA or methodologically through blocking/matching. 6) Select a design (e.g., RCT, pretest-posttest control group) inherently addressing anticipated validity threats. 7) Standardize procedures meticulously across sessions and groups.