Similar to Premium vs Sector, we have PB Premium vs Sub-sector as well. It is basically the stock PB ratio divided by the corresponding sub-sector PB ratio minus one. The interpretation is also similar to the premiums vs sector, but sometimes a sector is a very broad universe to compare. 

For instance, You can’t compare a 2 wheeler company’s PB with an Airline’s PB, but both are in the same sector. Hence, for users looking to find stock-specific investing opportunities in niche industries, this metric might be more helpful. However since stocks in a sub-sector are obviously less than a sector, this metric is susceptible to bias, where one or two companies could grossly affect the sub-sector’s average, but affecting the sector’s average might be tough since there are many more companies and more business varieties which won’t necessarily have correlated earning cycles.