As you know, most of the EOD data available have only OHLC price. I used to do back-testing using the Close price as both bid and ask. however, in real world, the bid and ask spread is huge and the bid/ask quantity is also never constant. Above that, the bid/ask price changes with every shares sold/bought. Therefore, my earlier back-test could never be implement in the real world. What approach should i do to get/estimate ask/bid price for backtesting for OHLC data?
There is a recent paper with a procedure to estimated the bid/ask spread from a series of daily high/low prices. Link: http://www3.nd.edu/~scorwin/papers/high-low_spreads.pdf