What is the difference between rational expectations and adaptive expectations?

Rational expectations is an economic theory that assumes individuals form their expectations about future events using all available information and making the best possible predictions. In this framework, people's expectations are unbiased and accurate. The premise is that agents will use all the relevant data, their past experience, and any new information to make decisions about the future. As new information becomes available, agents will update their expectations through this rational process. This concept was first proposed by John F. Muth in 1961.

Adaptive expectations is an economic theory that assumes people form their expectations about the future based on past experiences. The premise is that people adapt their expectations gradually as they observe new information over time. In this framework, people may not have complete information about future events or be capable of perfect rationality. As a result, they may be slow to adjust their expectations or may not always be accurate. This concept was introduced by Milton Friedman in 1957.

Now that we have defined both concepts, we can point out the main differences between rational and adaptive expectations: 1. Information Use: Rational expectations assume that people use all available information when forming expectations, while adaptive expectations assume people base their expectations primarily on past experiences. 2. Accuracy: Under rational expectations, people's expectations are assumed to be accurate and unbiased, whereas under adaptive expectations, people's expectations may be slow to adjust and may not always be accurate. 3. Speed of Adjustment: Rational expectations imply that people quickly adjust their expectations as new information becomes available, while adaptive expectations suggest a more gradual adjustment process. 4. Decision-Making Process: Rational expectations assume that people make decisions based on the best possible predictions using all available information. In contrast, adaptive expectations assume that people may not be capable of perfect rationality and may base their decisions on incomplete information. In summary, the main difference between the two theories lies in the formation process of expectations. Rational expectations assume unbiased and accurate expectations based on the use of all available information, while adaptive expectations attribute errors and bias to people's expectations due to their reliance on past experiences and the gradual adjustment of expectations over time.