This metric is used to measure under or outperformance of funds relative to their category average returns.
Formula : (5Y CAGR of the fund) / (5Y CAGR of the category average returns)
This metric is either at a premium i.e > 1 which represents that the fund has outperformed its category over the stated horizon or at a discount i.e <1 representing underperformance.
For example:
3Y CAGR of fund A is 22% vs its category average 3Y CAGR of 20% then Returns vs Sub-category returns : 3Y = 22%/20% = 1.1 ( at a premium ).