Which option correctly matches a bias with its mitigation strategy?

• A. Observer bias — accrual time adjustment
• B. Information bias — using unblinded assessments
• C. Selection bias — collecting only cross-sectional data
• D. Selection bias — randomization and allocation concealment

Answer: (D)

The main concept is how to prevent selection bias in study design. Selection bias happens when the groups being compared differ in important ways because of how participants are chosen or assigned, which can distort outcomes. The strongest way to prevent this is randomization, which helps balance both known and unknown confounders across groups, and allocation concealment, which stops investigators from influencing assignment. Together, they protect the study from systematic differences before the intervention begins.

Why this pairing is best: randomization assigns participants by chance, so each group is similar at the start, and allocation concealment prevents tampering or anticipation of assignments. That combination directly targets and minimizes selection bias.

Why the other options don’t fit: observer bias concerns how measurements are made and is best mitigated by blinding or standardized assessment, not accrual time adjustments. information bias arises from measurement errors; unblinded assessments can worsen it, whereas blinding helps reduce it. collecting only cross-sectional data does not reduce selection bias and can even introduce it, because the sample may not be representative of the whole population.

So, the correct pairing is selection bias with randomization and allocation concealment.