The requirements for a 'classical experimental' design include:

The requirements for a 'classical experimental' design include:

• A. Random assignment to treatment or control group
• B. Nonrandom assignment by self-selection into groups
• C. Use of a cross-sectional design
• D. Use of a convenience sample

Answer: (A)

Random assignment to treatment or control groups ensures equivalence between groups at baseline, which is essential for drawing causal conclusions in experimental research. By assigning participants by chance, you balance both known and unknown characteristics across groups, so differences observed after the intervention are more likely due to the treatment itself rather than preexisting factors. This control over selection bias is what makes a study capable of attributing causality to the manipulated variable. Nonrandom assignment by self-selection undermines internal validity because those who choose the treatment may differ in important ways (motivation, severity, demographic factors) that also influence outcomes, making it hard to determine what caused any observed effects. A cross-sectional design, capturing data at one moment, cannot establish temporal order or causality, which is why it’s not considered a classical experimental setup. A convenience sample affects how generalizable the findings are to broader populations, but in itself it doesn’t establish the controlled, randomized structure that defines classical experiments.

Random assignment to treatment or control groups ensures equivalence between groups at baseline, which is essential for drawing causal conclusions in experimental research. By assigning participants by chance, you balance both known and unknown characteristics across groups, so differences observed after the intervention are more likely due to the treatment itself rather than preexisting factors. This control over selection bias is what makes a study capable of attributing causality to the manipulated variable.

Nonrandom assignment by self-selection undermines internal validity because those who choose the treatment may differ in important ways (motivation, severity, demographic factors) that also influence outcomes, making it hard to determine what caused any observed effects. A cross-sectional design, capturing data at one moment, cannot establish temporal order or causality, which is why it’s not considered a classical experimental setup. A convenience sample affects how generalizable the findings are to broader populations, but in itself it doesn’t establish the controlled, randomized structure that defines classical experiments.