Question

What assumptions does the model of intertemporal choice make that are not likely true in the real world and would make the model harder to use in practice?

Short answer

The model of intertemporal choice makes several assumptions that are not likely true in the real world, which makes it harder to use in practice. These assumptions include perfect information, rationality, time consistency, a single utility function, and an infinite lifetime. In reality, consumers often face uncertainty and make irrational decisions, have time-inconsistent preferences, derive utility from multiple aspects of life, and have a finite lifespan. These real-world complexities limit the model's practicality and accuracy in representing actual consumer behavior.

Step-by-step solution

Assumption 1: Perfect Information

The model of intertemporal choice assumes perfect information. Consumers are assumed to know all the possible outcomes and risks associated with all their current and future consumption options. In the real world, however, this is often not the case because decisions are made under uncertainty due to lack of information or inaccurate predictions about the future.

Assumption 2: Rationality

The model assumes rational consumers, implying that individuals always make decisions that provide them with the highest utility, considering both present and future consumption. However, this assumption is often violated in the real world where consumers might give into temptations and make irrational decisions, leading to inconsistency in their choices across time.

Assumption 3: Time Consistency

In intertemporal choice, it’s assumed that a consumer’s preferences are time-consistent, meaning that their rate of time preference doesn’t change over time. However, in reality, consumers might be time-inconsistent, exhibiting a tendency to increasingly prefer present consumption as a given point in time becomes more imminent, pulling away from their once long-term oriented decisions.

Assumption 4: Single Utility Function

The model assumes that consumers derive their well-being based on a single utility function. However, in reality, different aspects such as health, social interactions and personal development may impact a person's utility, leading to multiple utility functions, which complicates the model.

Assumption 5: Infinite Lifetime

Another assumption is that consumers live infinitely, allowing them to smooth consumption over an infinite number of periods. This assumption clearly doesn't hold in the real world, as human lifespan is finite. The assumption simplifies the model but can distort important aspects of reality, such as individuals saving for retirement or life insurance. These assumptions, while necessary for simplifying the model, limit the model's practicality in illustrating real-world phenomena accurately.

Key concepts

Perfect Information

The concept of perfect information in the context of intertemporal choice implies that individuals have complete and accurate knowledge about all possible risks and outcomes related to both current and future consumption choices. In an ideal scenario, a consumer could precisely predict market trends, economic conditions, and personal financial status across an indefinite timeline. This assumption is crucial for making optimal intertemporal decisions.
However, in reality:

• Information is often incomplete. Consumers might not have access to all the data needed to make a thoroughly informed decision.
• Information may be misleading or biased, leading to errors in judgment.
• Future conditions are inherently uncertain and predicting them accurately can be difficult.

Thus, while perfect information simplifies the theoretical model, its departure from real-world scenarios can limit its applicability.

Rationality

Rationality within intertemporal choice models refers to the idea that consumers consistently make choices that maximize their utility or well-being. This means they would logically weigh costs and benefits of consumption across time, without being swayed by emotional motives or cognitive errors.
In practical terms, this assumption implies that:

• Consumers can perfectly calculate future utilities of all options available.
• Decisions are made purely based on logical analysis without biases.
• There is an element of self-control over impulses that may encourage immediate gratification at the expense of future benefits.

However, consumer behavior often diverges due to emotional impulses, cognitive biases, or lack of foresight, making this assumption less applicable in real life.

Time Consistency

Time consistency is an assumption that a consumer's preferences remain stable over time, implying that the way they value present versus future consumption does not change. If preferences are time-consistent, a decision made today regarding future consumption will remain valid in the future when the consumption period arrives.
Real-world scenarios show that:

• People may prefer something more immediate as the actual decision time approaches, deviating from prior plans.
• Immediate rewards often gain more appeal over time, known as present-biased preferences.
• Life changes can alter individual priorities and preferences, introducing time-inconsistency.

This discrepancy between the theoretical model and real behavior highlights one of the limitations of relying on time consistency as an assumption in intertemporal modeling.

Utility Function

In the intertemporal choice models, a single utility function is assumed to evaluate the satisfaction or happiness derived from consumption across different time periods. This approach simplifies comparisons and decision-making by assigning a single numerical satisfaction score to various consumption choices.
However, in the real world:

• Different factors influence satisfaction and well-being, such as health, social connections, and personal achievements.
• A single utility function fails to capture the multi-dimensional nature of human satisfaction.
• Multiple competing objectives can exist, each with its own utility consideration, complicating decision processes.

Thus, the singular utility function assumption may oversimplify the richness and complexity of human experience, impacting the validity of the model.

Infinite Lifetime

The assumption of an infinite lifetime in intertemporal choice models allows individuals to plan consumption as if they will live forever. This offers a simplified framework where consumers can seamlessly spread their resources over an endless horizon.
However, real-life does not support this assumption due to:

• Finite human lifespans that necessitate planning for end-of-life needs like retirement or savings.
• Events like illness or death that can induce sudden shifts in financial needs.
• The fact that the value placed on current versus future consumption changes as one's life progresses and time becomes a more limited resource.

While an infinite horizon reduces the complexity of calculations in models, it moves away from realistic scenarios where individuals must make decisions with knowledge of their finite lifespan.