How Permanent Income Hypothesis/Buffer Stock Model of Milton Friedman Got Nailed?

Milton Friedman and his gang at Chicago, including the ‘boys’ that went back and put their ‘free market’ wrecking ball through Chile under the butcher Pinochet, have really left a mess of confusion and lies behind in the hallowed halls of the academy, which in the 1970s seeped out, like slime, into the central banks and the treasury departments of the world. The overall intent of the literature they developed was to force governments to abandon so-called fiscal activism (the discretionary use of government spending and taxation policy to fine-tune total spending so as to achieve full employment), and, instead, empower central banks to disregard mass unemployment and fight inflation first. Wow!, Billy, these aren’t the usual contretemps and are wittily vitriolic. Several strands of their work – the Monetarist claim that aggregate policy should be reduced to a focus on the central bank controlling the money supply to control inflation (the market would deliver the rest (high employment and economic growth, etc); the promotion of a ‘natural rate of unemployment’ such that governments who tried to reduce the unemployment rate would only accelerate inflation; and the so-called Permanent Income Hypothesis (households ignored short-term movements in income when determining consumption spending), and others – were woven together to form a anti-government phalanx. Later, absurd notions such as rational expectations and real business cycles were added to the litany of Monetarist myths, which indoctrinated graduate students (who became policy makers) even further in the cause. Over time, his damaging legacy has been eroded by researchers and empirical facts but like all tight Groupthink communities the inner sanctum remain faithful and so the research findings haven’t permeated into major shifts in the academy. It will come – but these paradigm shifts take time.

Recently, another of Milton’s legacy bit the dust, thanks to a couple of Harvard economists, Peter Ganong and Pascal Noel, who with their paper “How does unemployment affect consumer spending?” smashed to smithereens the idea that households would not take consumption decisions with discretion, which the Chicagoan held to be a pivot of his active fiscal policy. Time traveling back to John Maynard Keynes, who outlined in his 1936 The General Theory of Employment, Interest and Money a view that household consumption was dependent on disposable income, and, that in times of economic downturn, the government could stimulate employment and income growth using fiscal policy, which would boost consumption.

In Chapter 3 The Principle of Effective Demand, Keynes wrote:

When employment increases, aggregate real income is increased. The psychology of the community is such that when aggregate real income is increased aggregate consumption is increased, but not by so much as income …

The relationship between the community’s income and what it can be expected to spend on consumption, designated by D1, will depend on the psychological characteristic of the community, which we shall call its propensity to consume. That is to say, consumption will depend on the level of aggregate income and, therefore, on the level of employment N, except when there is some change in the propensity to consume.

Keynes later (in Chapter 6 The Definition of Income, Saving and Investment) considered factors that might influence the decision to consume and talked about “how much windfall gain or loss he is making on capital account”.

He elaborated further in Chapter 8 The Propensity to Consume … and wrote:

The amount that the community spends on consumption obviously depends (i) partly on the amount of its income, (ii) partly on the other objective attendant circumstances, and (iii) partly on the subjective needs and the psychological propensities and habits of the individuals composing it and the principles on which the income is divided between them (which may suffer modification as output is increased).

And concluded that:

1. An increase in the real wage (and hence real income at each employment level) will “change in the same proportion”.

2. A rise in the difference between income and net income will influence consumption spending.

3. “Windfall changes in capital-values not allowed for in calculating net income. These are of much more importance in modifying the propensity to consume, since they will bear no stable or regular relationship to the amount of income.” So, wealth changes will impact positively on consumption (up and down).

Later, as he was reflecting in Chapter 24 on the “Social Philosophy towards which the General Theory might lead” he wrote:

… therefore, the enlargement of the functions of government, involved in the task of adjusting to one another the propensity to consume and the inducement to invest, would seem to a nineteenth-century publicist or to a contemporary American financier to be a terrific encroachment on individualism, I defend it, on the contrary, both as the only practicable means of avoiding the destruction of existing economic forms in their entirety and as the condition of the successful functioning of individual initiative.

For if effective demand is deficient, not only is the public scandal of wasted resources intolerable, but the individual enterpriser who seeks to bring these resources into action is operating with the odds loaded against him …

It was thus clear – that active fiscal policy was the “only practicable means of avoiding the destruction” of recession brought about by shifts in consumption and/or investment. That view dominated macroeconomics for several decades.

Then in 1957, Milton Friedman advocated the idea of Permanent income hypothesis. The central idea of the permanent-income hypothesis, proposed by Milton Friedman in 1957, is simple: people base consumption on what they consider their “normal” income. In doing this, they attempt to maintain a fairly constant standard of living even though their incomes may vary considerably from month to month or from year to year. As a result, increases and decreases in income that people see as temporary have little effect on their consumption spending. The idea behind the permanent-income hypothesis is that consumption depends on what people expect to earn over a considerable period of time. As in the life-cycle hypothesis, people smooth out fluctuations in income so that they save during periods of unusually high income and dissave during periods of unusually low income. Thus, a pre-med student should have a higher level of consumption than a graduate student in history if both have the same current income. The pre-med student looks ahead to a much higher future income, and consumes accordingly.Both the permanent-income and life-cycle hypotheses loosen the relationship between consumption and income so that an exogenous change in investment may not have a constant multiplier effect. This is more clearly seen in the permanent-income hypothesis, which suggests that people will try to decide whether or not a change of income is temporary. If they decide that it is, it has a small effect on their spending. Only when they become convinced that it is permanent will consumption change by a sizable amount. As is the case with all economic theory, this theory does not describe any particular household, but only what happens on the average.The life-cycle hypothesis introduced assets into the consumption function, and thereby gave a role to the stock market. A rise in stock prices increases wealth and thus should increase consumption while a fall should reduce consumption. Hence, financial markets matter for consumption as well as for investment. The permanent-income hypothesis introduces lags into the consumption function. An increase in income should not immediately increase consumption spending by very much, but with time it should have a greater and greater effect. Behavior that introduces a lag into the relationship between income and consumption will generate the sort of momentum that business-cycle theories saw. A change in spending changes income, but people only slowly adjust to it. As they do, their extra spending changes income further. An initial increase in spending tends to have effects that take a long time to completely unfold. The existence of lags also makes government attempts to control the economy more difficult. A change of policy does not have its full effect immediately, but only gradually. By the time it has its full effect, the problem that it was designed to attack may have disappeared. Finally, though the life-cycle and permanent-income hypotheses have greatly increased our understanding of consumption behavior, data from the economy does not always fit theory as well as it should, which means they do not provide a complete explanation for consumption behavior.

The idea of a propensity to consume, which had been formalised in textbooks as the Marginal propensity to consume (MPC) – which described the extra consumption that would follow a $ of extra disposable income, was thrown out by Friedman.

The MPC concept – that households consume only a proportion of each extra $1 in disposable income received – formed the basis of the expenditure multiplier. Accordingly, if government deficit spending of, say $100 million, was introduced into a recessed economy, firms would respond by increasing output and incomes by that same amount $100 million. But the extra incomes paid out ($100 m) would stimulate ‘induced consumption’ spending equal to the MPC times $100m. If the MPC was, say, 0.80 (meaning 80 cents of each extra dollar received as disposable income would be spent) then the ‘second-round’ effect of the stimulus would be an additional $80 million in consumption spending (assuming that disposable and total income were the same – that is, assuming away the tax effect for simplicity). In turn, firms would respond and produce an additional $80 million in output and incomes, which would then create further induced consumption effects. Each additional increment, smaller than the last, because the MPC of 0.80 would mean some of the extra disposable income was being lost to saving. But it was argued that the higher the MPC, the greater the overall impact of the stimulus would be. Instead, Friedman claimed that consumption was not driven by current income (or changes in it) but, rather by expected permanent income.

Permanent income becomes an unobservable concept driven by expectations. It also leads to claims that households smooth out their consumption over their lifetimes even though current incomes can fluctuate. So when individuals are facing major declines in their current income – perhaps due to unemployment – they can borrow short-term to maintain the smooth pattern of spending and pay the credit back later, when their current income is in excess of some average expectation.

The idea led to a torrent of articles mostly mathematical in origin trying to formalise the notion of a permanent income. They were all the same – GIGO – garbage in, garbage out. An exercise in mathematical chess although in search of the wrong solution. But Friedman was not one to embrace interdependence. In the ‘free market’ tradition, all decision makers were rational and independent who sought to maximise their lifetime utility. Accordingly, they would borrow when young (to have more consumption than their current income would permit) and save over their lifetimes to compensate when they were old and without incomes. Consumption was strictly determined by this notion of a lifetime income.

Only some major event that altered that projection would lead to changes in consumption.

The Permanent Income Hypothesis is still a core component of the major DSGE macro models that central banks and other forecasting agencies deploy to make statements about the effectiveness of fiscal and monetary policy.

So it matters whether it is a valid theory or not. It is not just one of those academic contests that stoke or deflate egos but have very little consequence for the well-being of the people in general. The empirical world hasn’t been kind to Friedman across all his theories. But the Permanent Income Hypothesis, in particular, hasn’t done well in explaining the dynamics of consumption spending.

Getting back to the paper mentioned in the beginning, it finds deployment of a rich dataset arguing to point where the permanent income hypothesis of Friedman is nailed to the coffin. If the permanent income hypothesis was a good framework for understanding what happens to the consumption patterns of this cohort then we would expect a lot of smoothing going on and relatively stable consumption.

Individuals, according to Friedman, are meant to engage in “self-insurance” to insure against calamity like unemployment. The evidence is that they do not.

The researchers reject what they call the “buffer stock model” (which is a version of the permanent income hypothesis).

They find:

1. “Spending drops sharply at the onset of unemployment, and this drop is better explained by liquidity constraints than by a drop in permanent income or a drop in work-related expenses.”

2. “We find that spending on nondurable goods and services drops by $160 (6%) over the course of two months.”

3. “Consistent with liquidity constraints, we show that states with lower UI benefits have a larger drop in spending at onset.” In other words, the fiscal stimulus coming from the unemployment benefits attenuates the loss of earned income somewhat.

4. “As UI benefit exhaustion approaches, families who remain unemployed barely cut spending, but then cut spending by 11% in the month after benefits are exhausted.”

5. As it turns out the “When benefits are exhausted, the average family loses about $1,000 of monthly income … In the same month, spending drops by $260 (11%).”

6. They compare the “path of spending during unemployment in the data to three benchmark models and find that the buffer stock model fits better than a permanent income model or a hand-to-mouth model.”

The buffer stock model assumes that families smooth their consumption after an income shock by liquidating previous assets – “a key prediction of buffer stock models is that agents accumulate precautionary savings to self-insure against income risk.”

The researchers find that the:

the buffer stock model has two major failures – it predicts substantially more asset holdings at onset and it predicts that spending should be much smoother at benefit exhaustion.


7. Finally, the researchers found “that families do relatively little self-insurance when unemployed as spending is quite sensitive to current monthly income.” Families “do not prepare for benefit exhaustion”.


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