Consequently, much economic analysis incorporates expectations into the various models as a given variable, usually under the heading CETERIS PARIBUS, or by assuming that an individual acts in accordance with the RATIONAL EXPECTATION HYPOTHESIS. A further problem is that expectations involve a time period and much economic analysis is static, i.e. points of equilibrium may be observed but the route between them is considered irrelevant. (See COMPARATIVE STATIC ANALYSIS.)
Nevertheless, expectations have played a significant part in economic theory, most notably in the work of KEYNES. Expectations are a major variable, it is argued, in determining BUSINESS CYCLES and affecting the SPECULATIVE DEMAND for money. Expectations are also influential when dealing with the TERM STRUCTURE OF INTEREST RATE.
To incorporate expectations into economic theory, it is possible to treat individual behaviour as adaptive, as illustrated in the ADAPTIVE EXPECTATION HYPOTHESIS.
Although the concept is straightforward, future expectations being adapted from past and present experiences, the attempts to reflect reality have led to complex structures being formulated.
The simplest form of expectations models are extrapolative expectations models where people form expectations about a future economic event like inflation based upon their assumption that the past trend in inflation will continue into the future. See KEYNESIAN ECONOMICS, EXPECTATIONS-ADJUSTED/AUGMENTED PHILLIPS CURVE, SPECULATOR, ANTICIPATED INFLATION, TRANSMISSION MECHANISM.