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Economic forecasting is not a science

Prashanth Perumal in The Hindu

India lost its tag as the ‘world’s fastest-growing economy’ last month as its fourth quarter GDP growth fell to 6.1%, the slowest in two years. Very few economists expected the slowdown. In fact, most waited for the economy to rebound as it quickly healed from the impact of the demonetisation of high-value rupee notes in November. Critics of demonetisation felt vindicated, particularly after GDP figures for the third quarter suggested that the shocking, overnight move to demonetise had very little negative impact.

Yet, for all the sermon delivered by the country’s punditry, the fact remains that macroeconomic forecasting is a lousy business — regardless of who makes the predictions. For one, data cannot prove or disprove any hypothesis as they do not establish causation. The mere fact that growth slowed in the first full quarter after demonetisation does not prove decisively that the slowdown was caused by demonetisation. As some have speculated, the current slump in the growth rate may be a continuation of the trend of slowing growth witnessed even before demonetisation.

Nor does the unexpectedly strong GDP growth in the third quarter prove that demonetisation has had no negative impact on the economy. The economy is a complex organism with several variables working in tandem, which makes prediction an almost impossible task. This is in contrast to the physical sciences where controlled experiments allow scientists to tease out the influence of any variable.

Two, there are no constant relationships between variables when it comes to the economy that allow for making exact predictions. So, even if economists were to dig into historical data and find the exact impact that demonetisation has had on GDP growth, there is no guarantee that it would hold in the future. For instance, people’s expectations may change which makes them adapt to a cashless economy better, thus blunting the impact of demonetisation on GDP growth.

Three, macroeconomic forecasting is focussed to a very large extent on measuring things that are fundamentally immeasurable. When it comes to measuring GDP, for instance, the price that is assigned to a good as its value is arbitrarily decided by statisticians. This happens despite the fact that the value of any good lies in the eyes of the consumer. Finally, both innocent and political biases influence the process of official data collection to calculate GDP, a fact that raises questions about its reliability.
None of this is to say that economists can make no useful predictions. But such predictions are more likely to be qualitative rather than quantitative. Any wise economist could foresee that demonetisation would have a substantial impact on the economy; simply from the premise that money greases the wheels of commerce, so outlawing it would affect demand and create chaos across production lines. But trying to quantify its impact in terms of the exact percentage points of growth that would be shaved off GDP is a futile exercise.

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