Concentration risk is a concept that comes from banking. In simple terms, concentration risk reflects the extent to which bank's assets (loans) are distributed across the borrowers. Take an example of a bank which has 10 large borrowers with equivalent size loans extended to them. In this case, each borrower accounts for 10 percent of the bank total assets and bank's concentration ratio is 10% or 0.1. Now, suppose that another bank has 5 borrowers with equivalent loans. For the second bank, the concentration ratio is 0.2 or 20%. Concentration risk (exposure to a limited number of borrowers) is obviously higher in the latter bank than in the former.
Despite coming from banking, the concept of concentration risk applies to other organisations and sectors. For example, take suppliers of components to large companies, like Apple. For many of these suppliers, Apple represents the source of much of their revenues and, thus, they are exposed to the concentration risk. See this recent article for examples.
For sectors, as opposed to individual organisations, concentration risk relates to the distribution of sector earnings. And the latest FactSet report from April 7, 2017 shows just how concentrated the geographical distributions of earnings for S&P 500 are:
- With exception of Information Technology, not a single sector in the S&P 500 has aggregate revenues exposure to the U.S. market that is below 50%;
- Seven out of 11 sectors covered within S&P 500 have exposure concentration to the U.S. market in excess of 70%; and
- On the aggregate, 70% of revenues for the entire S&P 500 arise from within the U.S. markets.
In simple terms, S&P 500 is extremely vulnerable to the fortunes of the U.S. economy. Or put differently, there is a woeful lack of economic / revenue sources diversification in the S&P 500 companies.