effects

An effect is a change that follows a cause or an influence. In science and everyday use, effects describe what happens as a result of something else. Distinguishing effect from cause is essential for understanding relationships, testing hypotheses, and predicting outcomes.

Effects can be physical, biological, social, or organizational. Physical effects include phenomena such as the Doppler effect, the photoelectric effect, refraction, or friction; they arise from the laws governing matter, energy, and motion. Biological and medical effects include responses to substances or procedures, such as the placebo effect, therapeutic effects, or adverse side effects. Social and economic effects cover outcomes of policies, technologies, or events, including spillovers, externalities, and unintended consequences.

Measuring effects often involves estimating effect sizes, statistical significance, and causal inference. Experimental designs such as randomized trials help establish causality by controlling confounding factors, while observational studies rely on methods to adjust for bias. Researchers distinguish association from causation, and may study effect modifiers—conditions that change the magnitude or direction of an effect.

In everyday language, the word "effect" is also used in contexts such as visual or audio effects in media, which create impressions or emphasize elements without altering underlying reality.

Overall, effects are central to understanding how acting on one thing can produce changes in another, whether in science, policy, health, or daily life.