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.