Differentiate simple randomization from block randomization.

• A. Simple randomization assigns by chance; block randomization ensures balance within blocks.
• B. Block randomization ignores group sizes; simple randomization balances groups.
• C. Simple randomization uses blocks; block randomization uses only chance.
• D. Block randomization eliminates bias entirely.

Answer: (A)

Simple randomization assigns participants to treatment groups purely by chance, like flipping a coin or using a random number generator. Block randomization, on the other hand, uses predefined blocks to keep the numbers in each group balanced as enrollment proceeds. For example, with blocks of four in a two-group trial, each block contains two people assigned to each group, which helps ensure equal group sizes throughout the recruitment process. This balance reduces the risk that a trial unintentionally ends up with one group larger than the other, especially in smaller studies or when enrollment is uneven. It’s worth noting that fixed blocks can make allocation more predictable if the block size is known, so researchers sometimes vary block sizes to preserve some allocation concealment. In short, one approach relies on chance alone, while the other imposes a structure to maintain balance within blocks.