Consumer Spending

Should you splurge on a restaurant meal or save money by eating at home? Should you buy a new car and, if so, how expensive a model? Should you redo that bathroom or live with it for another year? In the real world, households are constantly confronted with such choices—not just about the consumption mix but also about how much to spend in total. These choices, in turn, have a powerful effect on the economy: consumer spending normally accounts for two-thirds of total spending on final goods and services. In particular, as we’ve just seen, the decision about how much of an additional dollar in income to spend—the marginal propensity to consume—determines the size of the multiplier, which determines the ultimate effect on the economy of autonomous changes in spending.

But what determines how much consumers spend?

Current Disposable Income and Consumer Spending

The most important factor affecting a family’s consumer spending is its current disposable income—income after taxes are paid and government transfers are received. It’s obvious from daily life that people with high disposable incomes on average drive more expensive cars, live in more expensive houses, and spend more on meals and clothing than people with lower disposable incomes. And the relationship between current disposable income and spending is clear in the data.

The Bureau of Labor Statistics (BLS) collects annual data on family income and spending. Families are grouped by levels of before-tax income, and after-tax income for each group is also reported. Since the income figures include transfers from the government, what the BLS calls a household’s after-tax income is equivalent to its current disposable income.

Figure 11-2 is a scatter diagram illustrating the relationship between household current disposable income and household consumer spending for American households by income group in 2013. For example, point A shows that in 2013 the middle fifth of the population had an average current disposable income of $45,826 and average spending of $42,495. The pattern of the dots slopes upward from left to right, making it clear that households with higher current disposable income had higher consumer spending.

Current Disposable Income and Consumer Spending for American Households in 2013 For each income group of households, average current disposable income in 2012 is plotted versus average consumer spending in 2013. For example, the middle income group, with current disposable income of $40,187 to $65,501, is represented by point A, indicating a household average current disposable income of $45,826 and average household consumer spending of $42,495. The data clearly show a positive relationship between current disposable income and consumer spending: families with higher current disposable income have higher consumer spending.Source: Bureau of Labor Statistics.
During recessions, consumers tend to avoid higher-priced brand-name goods in favor of generics that cost less.

It’s very useful to represent the relationship between an individual household’s current disposable income and its consumer spending with an equation. The consumption function is an equation showing how an individual household’s consumer spending varies with the household’s current disposable income. The simplest version of a consumption function is a linear equation:

The consumption function is an equation showing how an individual household’s consumer spending varies with the household’s current disposable income.

where lowercase letters indicate variables measured for an individual household.

In this equation, c is individual household consumer spending and yd is individual household current disposable income. Recall that MPC, the marginal propensity to consume, is the amount by which consumer spending rises if current disposable income rises by $1. Finally, a is a constant term—individual household autonomous consumer spending, the amount of spending a household would do if it had zero disposable income. We assume that a is greater than zero because a household with zero disposable income is able to fund some consumption by borrowing or using its savings. Notice, by the way, that we’re using y for income. That’s standard practice in macroeconomics, even though income isn’t actually spelled “yncome.” The reason is that I is reserved for investment spending.

Recall that we expressed MPC as the ratio of a change in consumer spending to the change in current disposable income. We’ve rewritten it for an individual household as Equation 11-6:

Multiplying both sides of Equation 11-6 by Δyd, we get:

Equation 11-7 tells us that when yd goes up by $1, c goes up by MPC × $1.

Figure 11-3 shows what Equation 11-5 looks like graphically, plotting yd on the horizontal axis and c on the vertical axis. Individual household autonomous consumer spending, a, is the value of c when yd is zero—it is the vertical intercept of the consumption function, cf. MPC is the slope of the line, measured by rise over run. If current disposable income rises by Δyd, household consumer spending, c, rises by Δc. Since MPC is defined as Δcyd, the slope of the consumption function is:

The Consumption Function The consumption function relates a household’s current disposable income to its consumer spending. The vertical intercept, a, is individual household autonomous consumer spending: the amount of a household’s consumer spending if its current disposable income is zero. The slope of the consumption function line, cf, is the marginal propensity to consume, or MPC: of every additional $1 of current disposable income, MPC × $1 is spent.

In reality, actual data never fit Equation 11-5 perfectly, but the fit can be pretty good. Figure 11-4 shows the data from Figure 11-2 again, together with a line drawn to fit the data as closely as possible. According to the data on households’ consumer spending and current disposable income, the best estimate of a is $19,343 and of MPC is 0.50. So the consumption function fitted to the data is:

c = $19,343 + 0.50 × yd

A Consumption Function Fitted to Data The data from Figure 11-2 are reproduced here, along with a line drawn to fit the data as closely as possible. For American households in 2013, the best estimate of the average household’s autonomous consumer spending, a, is $19,343 and the best estimate of MPC is 0.50.Source: Bureau of Labor Statistics.

That is, the data suggest a marginal propensity to consume of approximately 0.50. This implies that the marginal propensity to save (MPS)—the amount of an additional $1 of disposable income that is saved—is approximately 0.50, and the multiplier is approximately 1/0.50 = 2.00.

It’s important to realize that Figure 11-4 shows a microeconomic relationship between the current disposable income of individual households and their spending on goods and services. However, macroeconomists assume that a similar relationship holds for the economy as a whole: that there is a relationship, called the aggregate consumption function, between aggregate current disposable income and aggregate consumer spending. We’ll assume that it has the same form as the household-level consumption function:

The aggregate consumption function is the relationship for the economy as a whole between aggregate current disposable income and aggregate consumer spending.

Here, C is aggregate consumer spending (called just “consumer spending”); YD is aggregate current disposable income (called, for simplicity, just “disposable income”); and A is aggregate autonomous consumer spending, the amount of consumer spending when YD equals zero. This is the relationship represented in Figure 11-5 by CF, analogous to cf in Figure 11-3.

Shifts of the Aggregate Consumption Function Panel (a) illustrates the effect of an increase in expected aggregate future disposable income. Consumers will spend more at every given level of aggregate current disposable income, YD. As a result, the initial aggregate consumption function CF1, with aggregate autonomous consumer spending A1, shifts up to a new position at CF2 and aggregate autonomous consumer spending A2. An increase in aggregate wealth will also shift the aggregate consumption function up. Panel (b), in contrast, illustrates the effect of a reduction in expected aggregate future disposable income. Consumers will spend less at every given level of aggregate current disposable income, YD. Consequently, the initial aggregate consumption function CF1, with aggregate autonomous consumer spending A1, shifts down to a new position at CF2 and aggregate autonomous consumer spending A2. A reduction in aggregate wealth will have the same effect.

Shifts of the Aggregate Consumption Function

The aggregate consumption function shows the relationship between disposable income and consumer spending for the economy as a whole, other things equal. When things other than disposable income change, the aggregate consumption function shifts. There are two principal causes of shifts of the aggregate consumption function: changes in expected future disposable income and changes in aggregate wealth.

Changes in Expected Future Disposable Income Suppose you land a really good, well-paying job on graduating from college in May—but the job, and the paychecks, won’t start until September. So your disposable income hasn’t risen yet. Even so, it’s likely that you will start spending more on final goods and services right away—maybe buying nicer work clothes than you originally planned—because you know that higher income is coming.

Conversely, suppose you have a good job but learn that the company is planning to downsize your division, raising the possibility that you may lose your job and have to take a lower-paying one somewhere else. Even though your disposable income hasn’t gone down yet, you might well cut back on spending even while still employed, to save for a rainy day.

Both of these examples show how expectations about future disposable income can affect consumer spending. The two panels of Figure 11-5, which plot disposable income against consumer spending, show how changes in expected future disposable income affect the aggregate consumption function. In both panels, CF1 is the initial aggregate consumption function. Panel (a) shows the effect of good news: information that leads consumers to expect higher disposable income in the future than they did before.

Consumers will now spend more at any given level of current disposable income, YD, corresponding to an increase in A, aggregate autonomous consumer spending, from A1 to A2. The effect is to shift the aggregate consumption function up, from CF1 to CF2. Panel (b) shows the effect of bad news: information that leads consumers to expect lower disposable income in the future than they did before. Consumers will now spend less at any given level of current disposable income, YD, corresponding to a fall in A from A1 to A2. The effect is to shift the aggregate consumption function down, from CF1 to CF2.

In a famous 1956 book, A Theory of the Consumption Function, Milton Friedman showed that taking the effects of expected future income into account explains an otherwise puzzling fact about consumer behavior. If we look at consumer spending during any given year, we find that people with high current income save a larger fraction of their income than those with low current income. (This is obvious from the data in Figure 11-4: people in the highest income group spend considerably less than their income; those in the lowest income group spend more than their income.) You might think this implies that the overall savings rate will rise as the economy grows and average current incomes rise; in fact, however, this hasn’t happened.

Friedman pointed out that when we look at individual incomes in a given year, there are systematic differences between current and expected future income that create a positive relationship between current income and the savings rate. On one side, people with low current incomes are often having an unusually bad year. For example, they may be workers who have been laid off but will probably find new jobs eventually. They are people whose expected future income is higher than their current income, so it makes sense for them to have low or even negative savings. On the other side, people with high current incomes in a given year are often having an unusually good year. For example, they may have investments that happened to do extremely well. They are people whose expected future income is lower than their current income, so it makes sense for them to save most of their windfall.

When the economy grows, by contrast, current and expected future incomes rise together. Higher current income tends to lead to higher savings today, but higher expected future income tends to lead to less savings today. As a result, there’s a weaker relationship between current income and the savings rate.

Friedman argued that consumer spending ultimately depends mainly on the income people expect to have over the long term rather than on their current income. This argument is known as the permanent income hypothesis.

Changes in Aggregate Wealth Imagine two individuals, Maria and Mark, both of whom expect to earn $30,000 this year. Suppose, however, that they have different histories. Maria has been working steadily for the past 10 years, owns her own home, and has $200,000 in the bank. Mark is the same age as Maria, but he has been in and out of work, hasn’t managed to buy a house, and has very little in savings. In this case, Maria has something that Mark doesn’t have: wealth. Even though they have the same disposable income, other things equal, you’d expect Maria to spend more on consumption than Mark. That is, wealth has an effect on consumer spending.

The effect of wealth on spending is emphasized by an influential economic model of how consumers make choices about spending versus saving called the life-cycle hypothesis. According to this hypothesis, consumers plan their spending over a lifetime, not just in response to their current disposable income. As a result, people try to smooth their consumption over their lifetimes—they save some of their current disposable income during their years of peak earnings (typically occurring during a worker’s 40s and 50s) and during their retirement live off the wealth they accumulated while working. We won’t go into the details of this hypothesis but will simply point out that it implies an important role for wealth in determining consumer spending. For example, a middle-aged couple who have accumulated a lot of wealth—who have paid off the mortgage on their house and already own plenty of stocks and bonds—will, other things equal, spend more on goods and services than a couple who have the same current disposable income but still need to save for their retirement.

Because wealth affects household consumer spending, changes in wealth across the economy can shift the aggregate consumption function. A rise in aggregate wealth—say, because of a booming stock market—increases the vertical intercept A, aggregate autonomous consumer spending. This, in turn, shifts the aggregate consumption function up in the same way as does an expected increase in future disposable income. A decline in aggregate wealth—say, because of a fall in housing prices as occurred in 2008—reduces A and shifts the aggregate consumption function down.

ECONOMICS in Action: Famous First Forecasting Failures

Famous First Forecasting Failures

The Great Depression created modern macroeconomics. It also gave birth to the modern field of econometrics—the use of statistical techniques to fit economic models to empirical data. The aggregate consumption function was one of the first things econometricians studied. And, sure enough, they quickly experienced one of the first major failures of economic forecasting: consumer spending after World War II was much higher than estimates of the aggregate consumption function based on prewar data would have predicted.

Figure 11-6 tells the story. Panel (a) shows aggregate data on disposable income and consumer spending from 1929 to 1941, measured in billions of 2005 dollars. A simple linear consumption function, CF1, seems to fit the data very well. And many economists thought this relationship would continue to hold in the future. But panel (b) shows what actually happened in later years. The points in the circle at the left are the data from the Great Depression shown in panel (a). The points in the circle at the right are data from 1946 to 1960. (Data from 1942 to 1945 aren’t included because rationing during World War II prevented consumers from spending normally.) The solid line in the figure, CF1, is the consumption function fitted to 1929–1941 data. As you can see, post–World War II consumer spending was much higher than the relationship from the Depression years would have predicted. For example, in 1960 consumer spending was 13.5% higher than the level predicted by CF1.

Changes in the Aggregate Consumption Function Over TimeSource: Bureau of Economic Analysis.

Why was extrapolating from the earlier relationship so misleading? The answer is that from 1946 onward, both expected future disposable income and aggregate wealth were steadily rising. Consumers grew increasingly confident that the Great Depression wouldn’t reemerge and that the post–World War II economic boom would continue. At the same time, wealth was steadily increasing. As indicated by the dashed lines in panel (b), CF2 and CF3, the increases in expected future disposable income and in aggregate wealth shifted the aggregate consumption function up a number of times.

In macroeconomics, failure—whether of economic policy or of economic prediction—often leads to intellectual progress. The embarrassing failure of early estimates of the aggregate consumption function to predict post–World War II consumer spending led to important progress in our understanding of consumer behavior.

Quick Review

  • The consumption function shows the relationship between an individual household’s current disposable income and its consumer spending.

  • The aggregate consumption function shows the relationship between disposable income and consumer spending across the economy. It can shift due to changes in expected future disposable income and changes in aggregate wealth.

11-2

  1. Question 11.4

    Suppose the economy consists of three people: Angelina, Felicia, and Marina. The table shows how their consumer spending varies as their current disposable income rises by $10,000.

    1. Derive each individual’s consumption function, where MPC is calculated for a $10,000 change in current disposable income.

    2. Derive the aggregate consumption function.

  2. Question 11.5

    Suppose that problems in the capital markets make consumers unable either to borrow or to put money aside for future use. What implication does this have for the effects of expected future disposable income on consumer spending?

Solutions appear at back of book.