Zenith Optimedia predicts global ad expenditure will grow 4.2% in 2015 to $531 billion. Growth is forecast to be slower than previous estimates due to weakness in Latin America from low commodity prices and Brazil's economy. Ad markets are grouped into regional blocs based on geographical proximity and performance similarity. Forecasts are provided for each bloc between 2014-2017, with Fast-Track Asia expected to see the strongest growth while Eastern Europe & Central Asia will see declines due to issues in Russia, Ukraine, and Belarus.