Relative Income Hypothesis

The Relative Income Hypothesis, first developed by James S. Duesenberry in 1949, is a consumption theory that argues individuals’ consumption decisions are shaped not only by their absolute income levels but also by their income relative to that of other individuals in society. Duesenberry’s approach was formulated to address the limitations of the classical Keynesian absolute income hypothesis of his time.

Core Assumptions

The Relative Income Hypothesis is built upon several fundamental assumptions regarding consumption behavior:

1. Social Comparison (Demonstration Effect): When making consumption decisions, individuals consider not only their own needs but also the consumption levels they observe among those around them. As a result, an individual’s consumption level is closely linked to the consumption levels of others in similar income groups.
2. Habit Persistence: An individual’s consumption level is shaped by past consumption habits. Even when income declines, individuals find it difficult to reduce consumption significantly. This creates a form of stickiness or lag in consumption behavior.
3. Sensitivity to Income Distribution: Individuals evaluate increases in their income not in absolute terms but in relation to their position within the overall income distribution. This directly influences their saving and consumption decisions.

Mathematical Formulation

According to Duesenberry, consumption depends on an individual’s relative income, that is, the ratio of their own income to the average income level in society. In this context, the individual’s consumption function can be expressed as:

C = f(Yᵣ)

Here, C represents consumption and Yᵣ represents relative income. Relative income is based on the relationship between an individual’s own income and the average income of a reference group within society.

Theoretical Contributions and Criticisms

Duesenberry’s hypothesis diverges from the Keynesian Absolute Income Hypothesis in two key respects:

1. Consumption Is Not Independent: According to the Relative Income Hypothesis, individuals’ consumption decisions are not independent of one another. Social interaction plays a decisive role in shaping consumption behavior. In contrast, the Keynesian model assumes that consumption depends solely on an individual’s own income.
2. Consumption and Saving Behavior Are Persistent: The tendency of individuals to maintain their established consumption levels even when income falls distinguishes this theory from traditional models.

In this regard, the Relative Income Hypothesis offers a more realistic model of consumption by incorporating psychological and sociological factors. However, its empirical applicability has been challenged in some studies due to the complexity of quantitatively measuring interpersonal interactions.