Subadditivity Effect
Updated 2026-08-03
INTRODUCTION
English translation pending.
CORE DEFINITION
The subadditivity effect describes how people assign a lower probability to a general event than to the sum of its parts. Asked whether they will die in an accident, people give a modest figure; asked separately about car crashes, fires, and drowning, the added estimates exceed the general one. The core claim is that evaluation depends on the granularity of the question, because specific subcases are easier to imagine and are weighted individually. Key qualifications are that overlapping subcases must not be double-counted and that the effect can be exploited to inflate concern.
SCAFFOLDING EFFECT
Reduce cognitive load
- Choose the grain: decide whether to present a risk as one item or as its parts. - Enumerate the parts: list concrete subcases when you need the risk to feel real. - Guard the total: check for overlap so the sum does not overstate the true probability.
Anchor fast decisions
A general category is abstract, so evaluating it requires a single holistic judgment that tends to be conservative. Concrete subcases are easier to imagine, and each receives its own estimate; when those estimates are added, the total exceeds the holistic figure. The same mechanism works in reverse, since presenting a risk as one broad item makes it feel smaller, which is why framing granularity changes how much attention and budget a risk attracts.
MINIMUM ACTION
In progress 0/1Practice this model in one real situation:
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Source support: Explicit
- en.wikipedia.orghttps://en.wikipedia.org/wiki/Subadditivity_effectverified
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