Randomization techniques and blocking/stratification MCQs With Answer

Introduction: This collection of MCQs on Randomization techniques and Blocking/Stratification is tailored for M.Pharm students preparing for Clinical Research (MPP 104T). The questions emphasize core principles, practical implementation, and common pitfalls of randomization methods—simple, block, stratified, permuted and adaptive techniques—plus allocation concealment and logistical issues in trials. Each MCQ encourages deeper understanding of how choice of randomization affects balance of prognostic factors, bias prevention, and analysis. These items aim to build conceptual clarity and exam readiness by combining definition-level, applied, and scenario-based questions with clear, authoritative answers for self-assessment and revision.

Q1. What is the primary purpose of randomization in clinical trials?

• To increase sample size
• To ensure blinding of participants
• To balance known and unknown confounding variables across treatment groups
• To speed up recruitment

Correct Answer: To balance known and unknown confounding variables across treatment groups

Q2. Which of the following best describes simple randomization?

• Allocating subjects in fixed small groups called blocks
• Random allocation equivalent to repeated independent coin tosses for each subject
• Assigning treatments based on baseline covariates
• Using alternating assignment (every other patient)

Correct Answer: Random allocation equivalent to repeated independent coin tosses for each subject

Q3. Blocked (or block) randomization is primarily used to:

• Guarantee concealment of allocation sequence
• Ensure treatment groups are balanced at periodic stages of enrollment
• Stratify subjects by center
• Randomize clusters rather than individuals

Correct Answer: Ensure treatment groups are balanced at periodic stages of enrollment

Q4. In a permuted block randomization with two treatments and block size 4, which of the following is true?

• All possible sequences within a block keep treatment assignments equal in number
• Each block contains only one treatment repeated four times
• The block size must remain constant and known to investigators
• Permuted blocks eliminate the need for allocation concealment

Correct Answer: All possible sequences within a block keep treatment assignments equal in number

Q5. Which problem can arise if block size is fixed and known to recruiters in a blinded trial?

• Increased statistical power beyond design
• Predictability of upcoming allocations leading to selection bias
• Failure to achieve balance between centers
• Inflation of Type I error rate

Correct Answer: Predictability of upcoming allocations leading to selection bias

Q6. Stratified randomization is used to:

• Ensure identical sample sizes across trials
• Control and balance important prognostic variables across treatment groups
• Replace blocked randomization in small trials
• Eliminate the need for blinding observers

Correct Answer: Control and balance important prognostic variables across treatment groups

Q7. Which of the following is a limitation of overstratification (creating too many strata)?

• It reduces the need for randomization
• It can lead to small strata with inadequate balance and operational complexity
• It guarantees perfect balance for all covariates
• It simplifies analysis by removing the need to adjust for covariates

Correct Answer: It can lead to small strata with inadequate balance and operational complexity

Q8. Minimization as an allocation method is best described as:

• A purely unpredictable method equivalent to coin tosses
• A deterministic adaptive method that assigns each new subject to reduce imbalance across several covariates
• A variant of simple randomization with unequal allocation ratios
• A method to randomize groups instead of individuals

Correct Answer: A deterministic adaptive method that assigns each new subject to reduce imbalance across several covariates

Q9. Which approach combines stratification and blocking effectively in multicenter trials?

• Using central randomization with permuted blocks within each stratum (center-by-treatment strata)
• Applying simple randomization across all centers without stratification
• Alternating assignment within each center
• Cluster randomization ignoring center effects

Correct Answer: Using central randomization with permuted blocks within each stratum (center-by-treatment strata)

Q10. What is allocation concealment and why is it important?

• The process of hiding trial results from participants; it increases participant retention
• Keeping the sequence of future treatment allocations hidden from those enrolling participants; it prevents selection bias
• Blinding outcome assessors to treatment; it improves measurement precision
• Randomly assigning participants after outcome measurement; it ensures better balance

Correct Answer: Keeping the sequence of future treatment allocations hidden from those enrolling participants; it prevents selection bias

Q11. Which method provides robust allocation concealment in modern trials?

• Homework sealed envelopes handled by trial coordinators
• Centralized telephone or web-based randomization systems with secure authentication
• Investigators using a printed random list kept in their office
• Determining allocation by patient’s date of birth

Correct Answer: Centralized telephone or web-based randomization systems with secure authentication

Q12. In a 2:1 unequal allocation randomization, which statement is correct?

• Block randomization cannot be used
• Stratified randomization becomes impossible
• Block sizes should be multiples of the allocation ratio to maintain balance within blocks
• Treatment groups will always be perfectly balanced at every interim point

Correct Answer: Block sizes should be multiples of the allocation ratio to maintain balance within blocks

Q13. Which randomization approach helps when there are many important covariates but a small sample size?

• Simple randomization without stratification
• Overstratification with many small strata
• Covariate-adaptive methods such as minimization
• Cluster randomization by convenience

Correct Answer: Covariate-adaptive methods such as minimization

Q14. What is a potential drawback of minimization if used deterministically without a random element?

• It increases sample size requirements
• It can be fully predictable and thus susceptible to selection bias
• It ensures worse balance than simple randomization
• It prevents stratification by center

Correct Answer: It can be fully predictable and thus susceptible to selection bias

Q15. Which statement about stratification variables is correct?

• They should include every measured baseline variable regardless of prognostic importance
• They should be limited to a few strong prognostic variables to avoid excessive strata
• They must always be continuous variables
• They cannot include site or center in multicenter trials

Correct Answer: They should be limited to a few strong prognostic variables to avoid excessive strata

Q16. If a trial uses block randomization within strata, how should randomization lists be managed to avoid bias?

• Investigators should be given full printed lists for transparency
• Lists should be centrally stored and accessed via secure system with limited access
• Lists can be posted in the clinic for enrollments
• Every site should maintain its own unlocked randomization book

Correct Answer: Lists should be centrally stored and accessed via secure system with limited access

Q17. Which of the following is TRUE about cluster randomization compared with individual randomization?

• Cluster randomization always yields better balance of baseline covariates
• Cluster randomization randomizes groups (e.g., practices), requiring adjustment for intracluster correlation in analysis
• Blinding is impossible in cluster trials
• Block randomization cannot be used in cluster trials

Correct Answer: Cluster randomization randomizes groups (e.g., practices), requiring adjustment for intracluster correlation in analysis

Q18. Which random number generation approach is most appropriate for clinical trial randomization schedules?

• Manual dice rolls recorded in notebooks
• Pseudo-random number generators with documented seed and validated software or central systems
• Using patient phone numbers as seeds
• Non-reproducible ad hoc methods for each site

Correct Answer: Pseudo-random number generators with documented seed and validated software or central systems

Q19. When analyzing data from a stratified randomized trial, what should be considered in the statistical analysis?

• Ignoring stratification variables always gives unbiased estimates
• Accounting for stratification factors (e.g., by including them in the model) can improve precision and validity
• Stratification variables should be treated as outcomes
• Stratification prevents the need for any baseline covariate adjustment

Correct Answer: Accounting for stratification factors (e.g., by including them in the model) can improve precision and validity

Q20. Which operational practice helps prevent tampering with sequentially numbered sealed opaque envelopes used for allocation?

• Using thin paper envelopes and no signatures
• Numbering envelopes, using tamper-evident seals, and independent preparation with audit trail
• Allowing site staff to reorder envelopes to match convenience
• Keeping envelopes unlocked in the clinical room

Correct Answer: Numbering envelopes, using tamper-evident seals, and independent preparation with audit trail

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