Most ETFs have only been around for a couple of years. An example is GLD. However, spot gold price history is available for several decades. Stock indices, silver, real-estate, currencies, etc. have long histories. So we should be able to develop approximate trade statistics for long periods of time by associating either a spot price history or reconstructed history with individual ETFs. For country ETFs, use a stock market index local to the country modified by the local currency. This is the sort of project that the P123 community could help with i.e. volunteering to find and test high correlation associated indicators.