I have been working on a couple different algorithims for the past year and have backtested them all extensivily and they always give me the similar out comes. Today I backtested pretty much every algorithim I have and they all are performing considerably lower than before. Big changes like going from %100 return to -10% return I have old backtest of the exact same algos from as early as last week. Im not sure what I am missing here or if something has changed from the previous backtest or which numbers to trust.