bibas100, You are right. I was just trying to defend mick's decision of inculding another country's GDP there. Looking at the figures, perhaps India's GDP would be more relevant. Or even both US and India as US is a major economy upon which so many countries including India and China depend. Letting the research period be known to us ,eg. 2055-2060, would have made it more meaningful. Nevertheless, must be an interesting paper in it entirety.