1. Any events that predictably follow another event (or combination of events). Specific effects may be attributed to a determining cause (see also sufficient condition) or to contributory influences (see also causation; determinism; necessary condition).
2. The outcomes of an act of communication, as in Lasswell's famous formulation in 1948 that such acts can be described in terms of ‘who says what, in which channel, to whom, with what effect?’ Such effects may be planned or unplanned, short-term or long-term. The study of ‘the impact upon audiences’ is effect analysis: see effects tradition.
3. In the discourse of the effects tradition, any human behaviour or social phenomenon ascribed to the influence of the media (or advertising). See also attitudinal effects; behavioural effects; cognitive effects; hierarchy of effects; indirect effects; limited effects theory; primary and secondary effects; social effects; third-person effects.
4. In experimental research, consistent patterns of influence of one or more factors on another (see dependent and independent variables). The identification of causal effects is the primary focus of experiments.