Hello guys, I've elaborated some trading strategies for different stocks, and I have backtested them over the last 11 years. The results are very compelling. The problem is that when I test them over another period (1997-2007), the results get materially different and worse. What do you think about this problem ? What do you think would be the best way for proceeding ? Thank you for any advice.
If you'd be more specific I d appreciate. Thank u