Theory of planned behaviour
Intentions — shaped by attitudes, social norms, and perceived control — predict behavior.
What it means
The Theory of Planned Behaviour (TPB) holds that behavior follows most directly from a person's intention to perform it, and that intention is in turn determined by three factors: the person's attitude toward the behavior, subjective norms (perceived social pressure from important others), and perceived behavioral control (how easy or difficult the behavior is believed to be). It extends its predecessor, the Theory of Reasoned Action, precisely by adding perceived behavioral control to handle behaviors that are not entirely under a person's voluntary control. The mechanism is a reasoned, expectancy-value account: each determinant is built from underlying beliefs (about outcomes, about others' expectations, and about facilitating or impeding factors), and perceived control can also predict behavior directly, not only through intention. The model is one of the most widely used in health and consumer research, but its central limitation is the intention–behavior gap: intentions explain only part of the variance in actual behavior, since good intentions frequently fail to translate into action. It matters because it gives practitioners specific, measurable targets — beliefs, norms, and perceived control — to move when they want to change a behavior, while reminding them that shifting intention is necessary but not sufficient.
Examples
Whether someone exercises depends on liking exercise (attitude), believing important others expect it (norms), and feeling able to fit it in (perceived control).
Whether an employee reports a safety near-miss depends on thinking it useful (attitude), sensing the team expects it (norms), and believing the form takes two minutes (perceived control).
Someone intends to switch to a cheaper energy tariff because they like the savings and friends have switched — but low perceived control, 'the paperwork will be a nightmare', stops them.
First described in Icek Ajzen (1991).