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Posts Tagged ‘cumulative causation’

Irrational exuberance

Both the financial and goods markets are heavily influenced by sentiment. And such sentiment tends to be self-reinforcing. If consumers and investors are pessimistic, they will not spend and not invest. The economy declines and this further worsens sentiment and further discourages consumption and investment. Banks become less willing to lend and stock markets fall. The falling stock markets discourage people from buying shares and so share prices fall further. The despondency becomes irrational and greatly exaggerates economic fundamentals.

This same irrationality applies in a boom. Here it becomes irrational exuberance. A boom encourages confidence and stimulates consumer spending and investment. This further stimulates the boom via the multiplier and accelerator and further inspires confidence. Banks are more willing to lend, which further feeds the expansion. Stock markets soar and destabilising speculation further pushes up share prices. There is a stock market bubble.

But bubbles burst. The question is whether the current global stock market boom, with share prices reaching record levels, represents a bubble. One indicator is the price/earnings (PE) ratio of shares. This is the ratio of share prices to earnings per share. Currently the ratio for the US index, S&P 500, is just over 26. This compares with a mean over the past 147 years of 15.64. The current ratio is the third highest after the peaks of the early 2000s and 2008/9.

An alternative measure of the PE ratio is the Shiller PE ratio (see also). This is named after Robert Shiller, who wrote the book Irrational Exuberance. Unlike conventional PE ratios, which only look at average earnings over the past four quarters, the Shiller PE ratio uses average earnings over the past 10 years. “Because this factors in earnings from the previous ten years, it is less prone to wild swings in any one year.”

The current level of the Shiller PE ratio is 29.14, the third highest on record, this time after the period running up to the Wall Street crash of 1929 and the dot-com bubble of the late 1990s. The mean Shiller PE ratio over the past 147 years is 16.72.

So are we in a period of irrational exuberance? And are stock markets experiencing a bubble that sooner or later will burst? The following articles explore these questions.

2 Clear Instances of Irrational Exuberance Seeking Alpha, Jeffrey Himelson (12/2/17)
Promised land of Trumpflation-inspired global stimulus has been slow off the mark South China Morning Post, David Brown (20/2/17)
A stock market crash is a way off, but this boom will turn to bust The Guardian, Larry Elliott (16/2/17)
The “boring” bubble is close to bursting – the Unilever bid proves it MoneyWeek, John Stepek (20/2/17)


  1. Find out what is meant by Minksy’s ‘financial instability hypothesis’ and a ‘Minsky moment’. How might they explain irrational exuberance and the sudden turning point from a boom to a bust?
  2. Is it really irrational to buy shares with a very high PE ratio if everyone else is doing so?
  3. Why are people currently exuberant?
  4. What might cause the current exuberance to end?
  5. How does irrational exuberance affect the size of the multiplier?
  6. How might the behaviour of banks and other financial institutions contribute towards a boom fuelled by irrational exuberance?
  7. Compare the usefulness of a standard PE ratio with the Shiller PE ratio.
  8. Other than high PE ratios, what else might suggest that stock markets are overvalued?
  9. Why might a company’s PE ratio differ from its price/dividends ratio (see)? Which is a better measure of whether or not a share is overvalued?
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Being an economist

Is too much expected of economists? When economic forecasts turn out to be wrong, as they often are, economists are criticised for having inaccurate or unrealistic models. But is this a fair criticism?

The following article by Richard Whittle from Manchester Metropolitan University looks at what economists can and cannot do. The article highlights two key problems for economic forecasting.

The first concerns human behaviour, which is influenced by a whole range of factors and can change very rapidly in response to changing circumstances. Moods of optimism or pessimism can quickly spread in response to a news item, such as measures announced by Donald Trump or latest data on growth or the housing market.

The second concerns the whole range of possible economic shocks. Such shocks, by their very nature, are hard to predict and can quickly make forecasts wrong. They could be a surprise election result, a surprise government policy change, a natural disaster, a war or a series of terrorist attacks. And these shocks, in turn, affect human behaviour. Consumption and investment may rise or fall as the events affect confidence and herd behaviour.

But is it a fair criticism of economics that it cannot foretell the future? Do economists, as the article says, throw up their hands and curse economics as a futile endeavour? Not surprisingly, the answer given is no! The author gives an analogy with medicine.

A doctor cannot definitely prevent illness, but can offer advice on prevention and hopefully offer a cure if you do get ill. This is the same for the work economists do.

Economists can offer advice on preventing crises or slowdowns but cannot definitively prevent them from happening. Economists can also offer robust advice on restoring growth, although when the advice is that the economy has grown too fast and should slow, it is often not welcomed by policy makers.

Helping understanding the various drivers in an economy and how humans are likely to respond to various incentives is a key part of what economists do. But making predictions with 100% certainty is asking too much of economists.

And just as medical professionals can predict that if you smoke, eat unhealthy food or take no exercise you are likely to be less healthy and die younger, but cannot say precisely when an individual will die, so too economists can predict that certain policy measures are likely to increase or decrease GDP or employment or inflation, but they cannot say precisely how much they will be affected.

As the article says, “the true value of the economist lies not in mystical fortune telling, but in achieving a better understanding of the nature of the economies in which we live and work.”

How to be an economist in 2017 The Conversation, Richard Whittle (24/1/17)


  1. For what reasons has economics been ‘in crisis’? What is the solution to this crisis?
  2. Look at some macroeconomic forecasts for a country of your choice made two years ago for today (see, for example, forecasts made by the IMF, OECD or a central bank). How accurate were they? Explain any inaccuracies.
  3. To what extent is economic forecasting like weather forecasting?
  4. What is meant by cumulative causation? Give some examples. Why does cumulative causation make economic forecasting difficult?
  5. How is the increased usage of contactless card payments likely to affect spending patterns? Explain why.
  6. Why is it difficult to forecast the effects of Brexit?
  7. How can economic advisors help governments in designing policy?
  8. Why do people tend to overweight high probabilities and underweight low ones?
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