Is someone using flipped price level data for doubling amount of historical data?
Did it prove to be beneficial in out of sample results or is there some fundamental reason data would be wrong if inverted?
I've no idea what "flipping level" means. The historical DAILY data I have, same as what you get for free on YahooFinance, lists open, close, low, high and adjusted (for splits and dividends). I use close-to-close in my calculations. Have experimented with close-to-open and then open-to-close to double the amount of data but the figures didn't seem to change (for better or worse) so I reverted to the simpler approach.