Slide 1
Chance decides the assigned group
Random allocation assigns trial participants to comparison groups using chance. It prevents investigators from choosing a group based on a person’s apparent prospects.
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Without this safeguard, healthier participants might preferentially receive one intervention. Their better outcomes could then reflect their starting condition rather than the treatment being tested.
Slide 2
The aim is comparability on average
Randomization reduces systematic differences in known and unknown background factors. It does not guarantee perfectly matched groups in every trial.
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Chance imbalances remain possible, especially in small studies. Random assignment therefore supports a method of comparison; it does not promise that every characteristic will have identical values in the resulting groups.
Slide 3
The next assignment must stay hidden
Allocation concealment prevents people enrolling participants from knowing the next assignment. A random sequence can be undermined if it is predictable.
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Someone who knows the next group could influence when a participant enters the study. Protecting the sequence during recruitment is therefore different from generating that sequence correctly in the first place.
Slide 4
Assignment is not population sampling
Random allocation divides the enrolled participants among groups. It does not mean those participants were randomly selected from the entire population.
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A trial can have strong internal comparisons while enrolling a restricted population. Assessing applicability still requires examining ages, conditions, care settings and other features of the people studied.
Slide 5
Later conduct still matters
Randomization is an important starting safeguard. Missing outcomes, unequal follow-up or biased measurement can still weaken the eventual comparison.
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Good trial reports describe how assignment occurred and what happened afterward. The word randomized should prompt examination of the methods, rather than replace that examination.
Sources
- How Do Clinical Trials Work?
NCI, NIH
- Clinical Trials
NIH Office of Behavioral and Social Sciences Research