I have a portfolio selection algorithm I want to backtest, but I don't want to limit the inputs at any point in time. For example, I don't want to exclude the Japanese stock market, just because it hasn't done well in recent history.
Ideally, I'll have a pool of ETFs that: 1. Cover broad market segments (i.e. "US Stocks," "Commodities," "Precious Metals," "Japanese stocks," "US Real Estate." etc.) 2. Are fairly liquid 3. Have low expense ratios 4. (Most important) Closely track an index that has a long history (This allows for a longer backtest).
For example, SPY is perfect. It's large, liquid, covers a major segment of the market, it has a long history, and I can substitute the S&P500 index if I need to go back further than the 1990's. CEF might also be a good option, as it's large, liquid, covers gold and silver, and has a pretty long history (back to about 1986 it seems).
Any other obvious choices