Maxim Pinkovskiy, Xavier Sala-i-Martin, 18 May 2018

Purchasing power parities have been one of the successes of economic measurement. This column asks whether these adjustments are a better measure of the underlying economy than market exchange rates, whether our successive estimates of PPP are improving, and whether we should discard past PPPs when new data become available. Using a regression of night-time lights on PPP-adjusted GDP data, it argues that the answers are yes, yes, and (for now) yes. In fact, current estimates of prices now may be better estimates of past prices than estimates of those past prices made at the time.

Yin-Wong Cheung, Menzie Chinn, Xin Nong, 15 September 2016

As long as countries strive to reallocate aggregate demand in their own favour, disputes will arise regarding the degree to which currency values are 'fair'. This column argues that the Penn effect – the observation that the price level is higher in countries with higher per capita income – may not be a reliable method to discern the fair value of a currency. Different specifications and different datasets lead to different estimates of the degree of misalignment, for example for the Chinese renminbi.

Maxim Pinkovskiy, Xavier Sala-i-Martin, 26 June 2016

When it comes to measuring GDP, researchers tend to use the latest vintage of the Penn World Tables. However, competing series like the World Development Indicators (WDI) and changing methodologies between vintages mean this is not necessarily the best approach. This column assesses the relative performance of different GDP estimators using night-time lights as an unbiased predictor of the growth rates of unobserved true income. Newer versions of the Penn Tables are not necessarily improvements on their direct predecessors.  Newer versions of the WDI index, especially the 2011 vintage, appear generally better at measuring cross-country income differences.

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