Which study design helps prevent bias by keeping both participants and staff unaware of treatment allocation?

Which study design helps prevent bias by keeping both participants and staff unaware of treatment allocation?

• A. Blinded or masked study
• B. Single-blind study
• C. Double-blind or double masked study
• D. Placebo-controlled study

Answer: (C)

Masking treatment allocation to prevent bias is the key idea. When neither participants nor those administering the treatment know which group a participant is in, outcomes are less influenced by expectations or differential care. That level of concealment is what a double-blind or double masked study achieves, so it best prevents both performance bias and assessment bias. A single-blind design keeps only one side unaware—either the participant or the staff—so biases can still creep in from the aware party. The term blinded or masked can refer to either single or double scenarios, so it doesn’t by itself guarantee that both groups are unaware. A placebo-controlled study describes the use of a placebo as a comparator, but it doesn’t specify who is blinded; it could be blinded or not.

Masking treatment allocation to prevent bias is the key idea. When neither participants nor those administering the treatment know which group a participant is in, outcomes are less influenced by expectations or differential care. That level of concealment is what a double-blind or double masked study achieves, so it best prevents both performance bias and assessment bias.

A single-blind design keeps only one side unaware—either the participant or the staff—so biases can still creep in from the aware party. The term blinded or masked can refer to either single or double scenarios, so it doesn’t by itself guarantee that both groups are unaware. A placebo-controlled study describes the use of a placebo as a comparator, but it doesn’t specify who is blinded; it could be blinded or not.