Not all that many people are aware of quite how appallingly bad most economics statistics are. Not in the sense of it's terrible that the numbers are as they are, but that the numbers are generally so shoddily lashed together. And this is obviously going to be even more true in hte poorer parts of the world. A government that hasn't quite worked out how to collect the rubbish isn't going to be all that good at counting the people nor what they do or earn.
Gregory Clark (who you should remember from the excellent "A Farewell to Alms") has some new research out looking at the historic rates of social mobility. A good summation of that is here, in the NY Times. Worth reading that but the short version is that social mobility has been very low across societies and history. The current day is not real change from those historical numbers.