Which statement best describes random assignment and its threats in experiments?

Which statement best describes random assignment and its threats in experiments?

• A. Random assignment uses chance to place participants in conditions; threats include noncompliance, attrition, and imperfect randomization in small samples.
• B. Random assignment guarantees no bias and eliminates threats.
• C. Random assignment is only used in qualitative studies.
• D. Random assignment relies on predetermined order rather than chance.

Answer: (A)

Random assignment uses chance to place participants into different conditions, with the aim of making the groups as comparable as possible at the start so that observed effects can be attributed to the treatment rather than preexisting differences. Even with random assignment, threats to internal validity can arise: noncompliance, where participants don’t follow the assigned condition; attrition, where dropouts occur and unevenly affect groups; and imperfect randomization in small samples, which can leave the groups less equivalent than hoped. Because of these realities, random assignment does not guarantee zero bias. It’s a hallmark of quantitative experiments, not something used only in qualitative studies, and it relies on chance for allocation rather than a predetermined order.

Random assignment uses chance to place participants into different conditions, with the aim of making the groups as comparable as possible at the start so that observed effects can be attributed to the treatment rather than preexisting differences. Even with random assignment, threats to internal validity can arise: noncompliance, where participants don’t follow the assigned condition; attrition, where dropouts occur and unevenly affect groups; and imperfect randomization in small samples, which can leave the groups less equivalent than hoped. Because of these realities, random assignment does not guarantee zero bias. It’s a hallmark of quantitative experiments, not something used only in qualitative studies, and it relies on chance for allocation rather than a predetermined order.