Biotech successful rate is very low. Let put it at 10%. If I have 20 candidates right before FDA approval. I short all of them. The only 2 success case would go up 200% and the remained 18 would go down 50% on average. I would still win out than longing the stocks.

If I assume they all equal weighted (or I adjust them using the weighting factors for all the stocks based on their market potential). Let’s assume all 10 bucks.

2 stocks went up from $10 to $40 which gave $60

18 stocks went down 50% which gave me $90.