Bias: dilution effect

Purpose: To provide an understanding of the dilution effect and its impact on decision making.

Description: The dilution effect is a cognitive bias that occurs when we weigh up several pieces of information, some of which are relevant to a decision that we have to make and some of which are irrelevant.

It turns out that in making a decision we do not usually distinguish between the relevant and irrelevant information. Instead, having irrelevant information dilutes the value of the relevant information.

For example, when more side-effects of a drug are listed in the information provided, we worry less about the serious side effects than when only the serious side effects are listed.

Similarly, when we are assessing someone’s performance, we provide a different assessment for someone for whom we have relevant and irrelevant information than for someone for whom we have exactly the same relevant information only.

The dilution effect is also important when we are trying to make a persuasive case to influence a decision. Increasing the number of arguments in our case, especially if some of them are relatively weak, will not strengthen the case, but actively weaken it. Sticking to the strong arguments alone is likely to be more persuasive.

Reference: “The counterintuitive way to be more persuasive” by Niro Sivanathan was a talk at ‘TEDxLondonBusinessSchool’, London, UK in 2019. Video (11 minutes) online at either:

  1., or
  2. YouTube:

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Posted: February 2021
Last modified: February 2021