Revisiting the Use of ETFs to Construct an S&P 500 Portfolio
Comparing the performance of an equally weighted sector portfolio against an S&P 500 index fund over a 20-year period.
The S&P 500 index is comprised of 11 sectors, but they are not equally weighted. In fact, not even close.
The sector that currently has the largest impact on the S&P 500’s return is information technology (Table 1). As of March 31, 2025, this sector represented 29.6% of the market capitalization of the entire S&P 500. As a result, the stocks categorized in the information technology sector (currently 69 companies) determine nearly 30% of the entire index’s return. Said differently, roughly 14% of the 500 stocks in the index determine nearly one-third of its performance.
The table clearly shows that the performance of companies in the information technology, financials, health care and consumer discretionary sectors exerts a much greater impact on the performance of the S&P 500 than that of companies in the energy, utilities, real estate and materials sectors. This is the natural result of building an index that is market-cap weighted. Market cap is determined by multiplying a stock’s current price per share by how many shares are outstanding.
In this update to my November 2020 AAII Journal article, “The Benefits of Building Your Own S&P 500 Portfolio Sector by Sector,” I revisit the how a sector-based portfolio compares to a portfolio that just holds an S&P 500 fund.