Re: Pakistan average economic growth under different head of states:
You mean, world bank has its own data that they tabulated themselves from people on ground in Pakistan? 
Well, World bank only monitor data and take data given to them by Pakistan bureau of Statistics (PBS). PBS gets their data from various Pakistani departments, like State Bank of Pakistan (who know everything about money supply in the country and many more), CBR (that knows people drawing and spending income in the country and value of goods and services in the country produced, etc), plus different departments and ministries, etc.
World bank takes rupee value of GDP (and many other data) from PBS, than convert those data in dollars that they quote.
Only difference is that, to convert rupee into dollars, world bank uses Atlas method for conversion (that take into account average value of exchange rate over last 3 years), while most other institutions use average value of rupee exchange rate over last one year. PBS also use average exchange rate over last one years. World bank also used to take one year average value for conversion, but they changed that sometime back.
In the end, true value of any Pakistani financial data is value that comes from PBS (Pakistan Bureau of Statistics), State bank, or Pakistani state departments (depending on what type of data is quoted), that is taken by institutions all over the world, including World Bank, ADB, IMF, etc.