I have always heard as a general guideline that your portfolio should never exceed 25% of its capital in one sector, or around 10% in one stock. My question is, what necessarily constitutes a "sector". Is Energy (which can comprise of oil, natural gas, coal, uranium, etc) an industry or sector? Or are the types of energy I have in parenthesis the sectors? Is Metals (which can comprise of Steel, Copper, Gold, Silver, etc) an industry or sector? Or are the types of metals I have in parenthesis the sectors? I ask because I find myself lately being very heavy in commodities but am unsure on whether I am exposing myself to too many stocks that are in the same sector. It seems that there is a gray area in this matter. Even some have told me that "commodities" which would include everything in Energy and Metals is a sector. Any clarity that could be given would be great, thanks.
Gold Consumer Descretionary Consumer Staples Energy Financials Healthcare Industrials Basic Materials Technology Utilities Bonds International (Emerging Markets) - Spydertrader
A better way to think about it is to say have no more than 20% in any one IDEA. Sectors can be highly correlated.
There are sector portfolio definitions and historical returns at different levels of granularity at: http://mba.tuck.dartmouth.edu/pages/faculty/ken.french/data_library.html You can use the historical returns to get some idea of how different "max % of portfolio" rules would have done in the past with the different sector definitions.