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The mid-cap segment of the U.S. equity universe, as represented by the S&P MidCap 400^®, has historically offered distinct views in terms of concentration, sector weights and return drivers. This prompts an exploration of whether these trends are reflected in the S&P MidCap 400 Scored & Screened Index, which is a broad-based, market-cap-weighted index designed to measure the performance of securities meeting sustainability criteria, while maintaining similar overall industry group weights as the S&P MidCap 400.

Starting with concentration, Exhibit 1 illustrates the weight of the 10 largest stocks in the S&P MidCap 400 Scored & Screened Index since its launch on Jan. 11, 2021, to April 30, 2025. The average weight stood at 9.20%, slightly higher than the S&P MidCap 400’s 6.35%. However, this concentration was significantly lower than the S&P 500 Scored & Screened Index, where the 10 largest stocks accounted for an average weight of 37.82% versus 30.05% for the S&P 500^®. This indicates that while the S&P MidCap 400 Scored & Screened Index showed some concentration, it still retained greater diversification compared to its large-cap counterpart.

Next, we direct our attention to sectoral weights and their relation to excess return in the S&P MidCap 400 Scored & Screened Index versus the S&P MidCap 400. Exhibit 2 summarizes the results of the Brinson attribution analysis for the year ending April 30, 2025. The S&P MidCap 400 Scored & Screened Index outperformed the S&P MidCap 400 by 0.32%, primarily due to stock selection effects (0.29%) as opposed to sector weighting effects (0.03%). This aligns with the index’s construction methodology, which aims to maintain overall similar industry weights to the S&P MidCap 400.

Further analysis of excess returns reveals key distinctions between the S&P MidCap 400 Scored & Screened Index and its large-cap counterpart, the S&P 500 Scored & Screened Index. Exhibit 3 summarizes the results of a similar Brinson² attribution analysis and shows that the S&P 500 Scored & Screened Index underperformed the S&P 500 by 2.82% over the one-year period shown, primarily due to negative stock selection effects (-2.64%). Sector contributions varied significantly: the performance of the S&P MidCap 400 Scored & Screened Index was boosted by the Health Care (0.86%) sector, while Industrials (-0.64%) contributed negatively to performance (see Exhibit 2). Conversely, the S&P 500 Scored & Screened Index faced significant negative selection effects in Information Technology (-1.11%) and Communication Services (-1.09%), with only a minor negative stock selection effect from Health Care (-0.03%; see Exhibit 3).

In summary, past results underscore the distinct differences in concentration, sector exposures and return drivers between the S&P MidCap 400 Scored & Screened Index and the S&P 500 Scored & Screened Index, reflecting the historical trends in their respective broad market benchmarks. Given these insights, the S&P MidCap 400 Scored & Screened Index shows its potential as a diversified benchmark for the mid-cap U.S. equity universe while pursuing sustainability criteria.

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