Sector Concentration Risk: Look Beyond Industry Labels to Customers and Investment Cycles
Companies in different sectors can share exposure to the same customers and capital spending cycle. Calculate shared demand exposure and its contribution to portfolio losses.
Sector concentration risk arises when investments are clustered in a particular industry and are heavily affected by the same shock. Look beyond exchange sector classifications to end customers, revenue by region, and dependence on capital spending. When individual stocks and thematic ETFs expose you to the same industry, actual concentration exceeds the apparent allocation.
Find overlapping revenue exposure beyond sector classifications
A semiconductor manufacturer, an equipment supplier, and a company owning factory real estate can all be affected by a particular customer's expansion plans, even if their official sectors differ. Read each company's annual report for its major customers and sources of demand, and note when revenue is generated. Equipment orders move ahead of production expansion, while demand for consumables responds to capacity utilization. The timing of the impact may differ, but the shared cause remains. Do not treat investments as independent simply because their industry labels differ.
Distinguish concentration caused by price gains from new purchases
Even if you initially allocate evenly, a strong rally in one industry increases its share of market value. That concentration affects the risk of your actual assets even without additional purchases. Weights based only on original invested amounts miss this change. Calculate industry totals using current market values, and note whether a downturn in that industry would also affect your employment or business income. This gives a clearer view of your household's overall vulnerability.
Translate sector stress into its impact on total assets
You cannot assume that every stock falls by the same percentage when an industry weakens. Instead, assign different assumed declines to different industries and calculate total losses to assess sensitivity. Include a separate scenario in which industries with overlapping customers are hit simultaneously. Rather than relying solely on historically low correlations, explain how declining demand could flow through to each company's earnings and valuation multiples.
Align the valuation date for sector weights with the date of the holdings data. If ETF weights come from older data while directly held stocks use today's market values, the calculation is only a rough exposure estimate. If public information does not reveal customer revenue shares, do not invent precise figures; identify a separate group with potential exposure. Distinguishing known concentration from unverified concentration is more useful than excessive precision.
Worked example
Hypothetical example: Of KRW 20 million in total assets, you hold KRW 5 million in semiconductor stocks, KRW 3 million in equipment stocks, and KRW 4 million in a related ETF. Under the simplifying assumption that 75% of the ETF is exposed to the same demand cycle, the linked amount is KRW 11 million, or 55%. If this group falls 30% and the rest is unchanged, the loss is KRW 3.3 million, or 16.5% of the total. Actual ETF weights and company sensitivities must be checked separately.
What to check
- Have you checked end sources of demand beyond official sector classifications?
- Have you calculated weights using current market values rather than original invested amounts?
- Have you included the industry exposure of thematic ETFs?
- Are your salary and investment assets tied to the same industry?
Sources and primary materials
This is educational material about research methods. For an actual company decision, verify the filings and primary sources for the relevant period.