u/mrmrmrj ·
Reddit — r/ValueInvesting
· July 14, 2026 at 20:41
· ⬆ 15 pts
· 💬 14 comments
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AI Summary
Summary
Post summarizes an academic study (1971–2025) comparing passive "do-nothing" S&P 500 portfolios: equal-weighted beats value-weighted over the full sample; largest-stock portfolios recently outperformed but historically underperform; concentrated random portfolios rarely beat the index.
Author’s thesis: equal-weighting the entire index is the best long-term do-nothing strategy, while stock picking (concentrated portfolios) very rarely beats the index over long periods.
Quality assessment: This is a summary of an academic study with clear data and results – well-researched secondary analysis, not original DD or speculation.
Score15
Comments14
Upvote %86%
▶ Full Post Text
I am going to cut and paste the abstract summary below and then turn it into English:
Abstract:
I study outcomes for a variety of "do-nothing" portfolios constructed from constituents of the S&P 500 index, from 1971 to 2025. These portfolios maintain their positions even for those stocks that exit the index. The findings include (i) initially equal-weighted portfolios outperform initially value-weighted portfolios over the full sample period, (ii) value-weighted "do-nothing" portfolios essentially match the index on average, (iii) portfolios constructed from the largest constituent stocks have recently outperformed portfolios constructed from all index constituents, but this is atypical, as over the full sample the largest-stock portfolios performed quite poorly, and (iv) narrow portfolios of randomly selected component stocks generate average returns similar to the index, but underperform the majority of the time, and more so over longer periods and for narrow portfolios.
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(i) equal weighting every stock in the index from the starting period did the best
(ii) matching the market-weighted index (the way the index is currently constructed) matched the index. Of course it did since that is the way the index is constructed.
(iii) owning the largest mkt cap companies in the index was a bad idea even if it has been a very good idea most recently.
(iv) it is very hard to beat the equal weighted index with a more concentrated portfolio, i.e. stock picking consistently is very hard.