Estudio del sistema micelar

We introduce a novel and unifying explanation for “anomalies” in intertemporal choice and present empirical support for it. In the theoretical part of the paper, we find that subjective expectations can have significant effect on discounting behavior and drive sys-tematic departures from exponential discounting. We discuss one particular situation where such departures naturally occur. Limited access to liquidity can prevent impatient consumers with positive, rational expectations to reach a smooth consumption path. Opt-ing for new alternatives materializOpt-ing at dates where income is expected to be relatively low can help them to, at least partly, overcome these limitations. Our approach stands in contrast to Loewenstein and Prelec (1992) and others, who do not only criticize the assumptions underlying the exponential discounted utility model, but also argue that consumer’s preferences are the ultimate driver of “anomalies”. This is not the case in our model. The typical consumer may still comply with the standard assumptions, but the limitations imposed by the environment constrain her scope of action which may lead her to reveal anomalous behavior. Moreover, our approach is not a descriptive one, but, rather, it provides a clear intuition for why and by how much people depart from exponential discounting.

The results in the empirical part of the paper lend strong support for our hypothesis that subjective expectations govern intertemporal choice behavior. Subjects with positive income expectations and limited access to liquidity reveal much higher discount rates and a sharper decline of these rates in time horizon. The student group with higher estimated expectations also exhibits a more pronounced magnitude effect. An interesting insight is that the majority of empirical studies so far was conducted with relatively poor subjects, i.e. subjects who only hold few liquid assets and typically only have limited borrowing opportunities. Students, for example, are not only exceptionally exposed to such liquidity constraints, but usually also hold substantial positive income expectations. According to our model, we therefore expect them to depart much more strongly from exponential discounting than groups not holding such expectations or not facing such constraints. This should be taken into account when predicting behavior of other groups or recommending policies based on experimental findings.

Liquidity constraints may not be the only explanation for a link between subjective expectations and discounting behavior, however. Empirical evidence reports that people are often too optimistic when it comes to evaluating future life events (Weinstein, 1980, 1987; Armor and Taylor, 2002). People typically overestimate their future earnings

(Do-minitz, 1998) and their ability to resist future temptations (Nordgren et al., 2009). While such consumers obviously do not have rational expectations, this alternative explanation does not contradict our basic model. Having a too optimistic consumption plan can be sufficient to generate the typical “anomalies”, even if no liquidity constraints exist or the consumer is not sufficiently impatient.⁶⁷ Such consumers’ behavior, however, will never be dynamically consistent.

Our results have strong implications. The fact that rational planners, i.e. consumers with positive, rational expectations facing liquidity constraints, and myopic fools, i.e.

consumers with dynamically inconsistent preferences or too optimistic beliefs, can reveal observationally equivalent behavior poses important challenges for the prediction of be-havior and the design of suitable policies. One basic problem is that constant discount rates are no longer the proper criteria to identify rational types. Additional informa-tion about subjective expectainforma-tions and liquidity constraints may therefore be needed to make predictions. Similar problems arise when searching for policies which help irrational consumers to behave more rationally. Interventions not taking into account the different causes underlying behavior, may fail to have the desired effect, be a waste of money or even have detrimental effects for those consumers with rational intentions. Policies geared at undersavings, for example, should only affect those consumers not being aware of what they do, but not those with a rational plan and limited liquidity. Mechanisms distinguish-ing rational planners from myopic fools are therefore needed. Possible startdistinguish-ing points for the development of such mechanisms are these types’ different preferences for commitment and the dynamic consistency of their behavior. The rational consumer, for example, is willing to insure herself against exogenous income shocks, but not against her own future behavior. Conversely, hyperbolic or overoptimistic consumers should be concerned about their own behavior. Whether or not they show a preference for commitment, however, depends on their degree of sophistication (O’Donoghue and Rabin, 1999).

We see a number of directions our work may be extended to. First, our model gen-erates numerous sharp predictions not made by other discounting models. Examples are conditions for which we predict increasing discount rates, magnitude-dependency, the close connection between the “anomalies” or the effect subjective expectations have on behavior. These predictions are testable and make our model falsifiable.

Second, richer expectations (and possibly even liquidity constraints) data can help to

67Formally, ct> c0 ≥ 0 ∀t > 0 must hold. This does not necessarily require the consumer to have a precise consumption plan in mind. The consumer’s beliefs about the future, however, must imply that marginal utility derived from consumption is always larger today compared to tomorrow.

better understand how people’s beliefs govern behavior. There are a number of papers proposing methods to elicit subjective expectations (Dominitz and Manski, 1996, 1997;

Dominitz, 2001; Manski, 2004). Such procedures can be adopted to account for the magnitude, timing, uncertainty and heterogeneity of subjects’ expectations. Embedded in dynamic choice experiments, they can provide additional insights into how expectations are formed and how they drive consumer behavior.

Figure B.9: Positive Expectations and Prospect Arguments

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Figure B.10: Inferred Time Preferences

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· · ·expectations model — CRDI-model (c= 0)^!