Group polarization
Discussion pushes a group toward a more extreme version of its leaning.
What it means
Group polarization is the well-documented finding that after members deliberate together, the group's average position becomes more extreme in the direction it already leaned, rather than converging on a moderate middle. Two complementary mechanisms drive it: persuasive arguments — during discussion members hear a preponderance of novel reasons favoring the dominant view, which shifts everyone further that way — and social comparison, in which people, wanting to be seen favorably relative to the group, adjust their stated position toward the admired extreme. Originally noticed as the 'risky shift,' the effect was shown to run toward greater caution too when the group's initial tilt was cautious, establishing that it amplifies whatever direction already prevails. A key boundary condition is that polarization requires a pre-existing lean and genuine exchange; mixed groups with cross-cutting arguments tend to moderate instead, which is why deliberate viewpoint diversity is a practical antidote. It matters because polarization helps explain jury severity, escalating risk-taking by teams, online radicalization, and the hardening of opinion inside ideologically homogeneous echo chambers.
Examples
A jury that leans slightly toward conviction before deliberating often hardens, after discussion, into a confident and more severe consensus.
An investment club whose members already like a stock talks itself, over a single evening, into a far larger position than any one of them would have taken alone.
A forum for people mildly sceptical of a vaccine hardens over months into certainty, as every thread supplies fresh arguments for the existing lean and almost none against it.
First described in Moscovici & Zavalloni (1969); Stoner's risky shift.