Randomized controlled trials

What it means

A study that uses chance, like drawing lots, to decide who receives each option being compared. Researchers compare the groups’ outcomes to estimate the effect of those options.

Examples on this page are illustrations, not findings from the research cards.

Worked example

A lottery assigns volunteers to a training programme or a comparison group. Researchers then compare their outcomes.

Hypothetical example: 100 volunteers enter a lottery. It assigns 50 an offer of training and 50 to a comparison group. Six months later, researchers measure the same outcome in both groups. Assignment comes from the lottery rather than from who seems most motivated.

Suppose the training-offer group averages ₹500 more in monthly earnings. This is the observed difference to investigate, not proof of an exact ₹500 effect. Researchers must assess uncertainty, check how the trial was carried out and examine missing responses before interpreting it.

A closer look

A randomized controlled trial uses a chance process to assign people to the options being compared. This helps separate a programme's effect from differences in who chooses it or is selected for it. Random allocation makes groups comparable on average, including for characteristics researchers have not measured. It does not guarantee identical groups in any one trial, especially a small one.

Researchers compare the groups' outcomes to estimate the effect of the assigned options. The strength of that estimate still depends on how the trial is designed, carried out and analysed. Missing follow-up information, changes in what people receive and poor measurement can affect the findings. Random assignment is also different from randomly sampling people from a population: a trial's volunteers need not represent everyone.

A common misunderstanding

Random assignment does not guarantee identical groups, flawless follow-up, or findings that apply to everyone outside the trial.

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Sources

The wording and examples are original explanations informed by these references.

Cite this explanation

Randomized controlled trial. aikyam school. https://aikyam.school/glossary/randomized-trial/

Used in these cards

410 cards use this term

The original research wording is preserved in these cards.