{
  "title": "S&P 500 Concentration Research Series: Weight, Earnings, Valuation, and Forward Returns",
  "path": "/research/sp500-concentration-series",
  "publishedAt": "2026-09-21",
  "updatedAt": null,
  "dataAsOf": "2026-06-30",
  "version": "1.0",
  "studies": [
    {
      "slug": "historical-sp500-concentration",
      "path": "/research/historical-sp500-concentration",
      "title": "S&P 500 Concentration History: How the Top 10 Changed From 1965 to 2025",
      "role": "historical-structure",
      "question": "How did S&P 500 top-10 weight change across reproducible decade endpoints?",
      "dataAsOf": "2025-06-30",
      "version": "1.0",
      "downloads": {
        "json": "/research-data/historical-sp500-concentration-2025-06-30.json",
        "csv": "/research-data/historical-sp500-concentration-2025-06-30.csv"
      }
    },
    {
      "slug": "sp500-earnings-concentration",
      "path": "/research/sp500-earnings-concentration",
      "title": "S&P 500 Earnings Concentration: Are the Top 10 Backed by Profits?",
      "role": "earnings-support",
      "question": "How much of top-10 market-cap concentration was accompanied by trailing earnings concentration?",
      "dataAsOf": "2026-03-31",
      "version": "1.0",
      "downloads": {
        "json": "/research-data/sp500-earnings-concentration-2026-03-31.json",
        "csv": "/research-data/sp500-earnings-concentration-2026-03-31.csv"
      }
    },
    {
      "slug": "sp500-valuation-concentration",
      "path": "/research/sp500-valuation-concentration",
      "title": "S&P 500 Valuation Concentration: What Does the Index Cost Without the Top 10?",
      "role": "valuation-split",
      "question": "How different was top-10 forward P/E from the remaining companies?",
      "dataAsOf": "2026-06-30",
      "version": "1.0",
      "downloads": {
        "json": "/research-data/sp500-valuation-concentration-2026-06-30.json",
        "csv": "/research-data/sp500-valuation-concentration-2026-06-30.csv"
      }
    },
    {
      "slug": "sp500-concentration-forward-returns",
      "path": "/research/sp500-concentration-forward-returns",
      "title": "S&P 500 Concentration and Forward Returns: Does a Top-Heavy Market Predict the Next Decade?",
      "role": "forward-return-sensitivity",
      "question": "Did starting concentration show a stable relationship with the following decade return?",
      "dataAsOf": "2025-06-30",
      "version": "1.0",
      "downloads": {
        "json": "/research-data/sp500-concentration-forward-returns-2025-06-30.json",
        "csv": "/research-data/sp500-concentration-forward-returns-2025-06-30.csv"
      }
    }
  ],
  "synthesis": {
    "historical": {
      "june1965TopTenWeightPct": 38.24,
      "june2025TopTenWeightPct": 38.15,
      "sixtyYearChangePercentagePoints": -0.09,
      "finalDecadeIncreasePercentagePoints": 20.34
    },
    "earnings": {
      "date": "2026-03-31",
      "topTenMarketCapSharePct": 37.9,
      "topTenTrailingEarningsSharePct": 33.2,
      "capMinusEarningsGapPctPoints": 4.7,
      "gapNarrowingPctPoints": 3.3
    },
    "valuation": {
      "date": "2026-06-30",
      "topTenForwardPe": 21.6,
      "remainingForwardPe": 19.6,
      "topTenMinusRemainingForwardPe": 2,
      "spreadNarrowingForwardPe": 8.1
    },
    "forwardReturns": {
      "observationCount": 6,
      "pearsonCorrelation": -0.72,
      "pearsonExcluding1965": -0.04
    }
  },
  "metrics": [
    {
      "dimension": "historical-structure",
      "metric": "june-1965-top10-weight",
      "label": "June 1965 top-10 index weight",
      "value": 38.24,
      "unit": "percent",
      "asOfDate": "1965-06-30",
      "sourceStudySlug": "historical-sp500-concentration",
      "sourceStudyPath": "/research/historical-sp500-concentration"
    },
    {
      "dimension": "historical-structure",
      "metric": "june-2025-top10-weight",
      "label": "June 2025 top-10 index weight",
      "value": 38.15,
      "unit": "percent",
      "asOfDate": "2025-06-30",
      "sourceStudySlug": "historical-sp500-concentration",
      "sourceStudyPath": "/research/historical-sp500-concentration"
    },
    {
      "dimension": "historical-structure",
      "metric": "sixty-year-concentration-change",
      "label": "June 1965 to June 2025 top-10 weight change",
      "value": -0.09,
      "unit": "percentage-points",
      "asOfDate": "2025-06-30",
      "sourceStudySlug": "historical-sp500-concentration",
      "sourceStudyPath": "/research/historical-sp500-concentration"
    },
    {
      "dimension": "historical-structure",
      "metric": "final-decade-concentration-increase",
      "label": "June 2015 to June 2025 top-10 weight increase",
      "value": 20.34,
      "unit": "percentage-points",
      "asOfDate": "2025-06-30",
      "sourceStudySlug": "historical-sp500-concentration",
      "sourceStudyPath": "/research/historical-sp500-concentration"
    },
    {
      "dimension": "earnings-support",
      "metric": "march-2026-top10-market-cap-share",
      "label": "March 2026 top-10 market-cap share",
      "value": 37.9,
      "unit": "percent",
      "asOfDate": "2026-03-31",
      "sourceStudySlug": "sp500-earnings-concentration",
      "sourceStudyPath": "/research/sp500-earnings-concentration"
    },
    {
      "dimension": "earnings-support",
      "metric": "march-2026-top10-trailing-earnings-share",
      "label": "March 2026 top-10 trailing-earnings share",
      "value": 33.2,
      "unit": "percent",
      "asOfDate": "2026-03-31",
      "sourceStudySlug": "sp500-earnings-concentration",
      "sourceStudyPath": "/research/sp500-earnings-concentration"
    },
    {
      "dimension": "earnings-support",
      "metric": "march-2026-cap-minus-earnings-gap",
      "label": "March 2026 market-cap minus earnings-share gap",
      "value": 4.7,
      "unit": "percentage-points",
      "asOfDate": "2026-03-31",
      "sourceStudySlug": "sp500-earnings-concentration",
      "sourceStudyPath": "/research/sp500-earnings-concentration"
    },
    {
      "dimension": "earnings-support",
      "metric": "cap-minus-earnings-gap-narrowing",
      "label": "March 2024 to March 2026 gap narrowing",
      "value": 3.3,
      "unit": "percentage-points",
      "asOfDate": "2026-03-31",
      "sourceStudySlug": "sp500-earnings-concentration",
      "sourceStudyPath": "/research/sp500-earnings-concentration"
    },
    {
      "dimension": "valuation-split",
      "metric": "june-2026-top10-forward-pe",
      "label": "June 2026 top-10 forward P/E",
      "value": 21.6,
      "unit": "forward-pe",
      "asOfDate": "2026-06-30",
      "sourceStudySlug": "sp500-valuation-concentration",
      "sourceStudyPath": "/research/sp500-valuation-concentration"
    },
    {
      "dimension": "valuation-split",
      "metric": "june-2026-remaining-forward-pe",
      "label": "June 2026 remaining-company forward P/E",
      "value": 19.6,
      "unit": "forward-pe",
      "asOfDate": "2026-06-30",
      "sourceStudySlug": "sp500-valuation-concentration",
      "sourceStudyPath": "/research/sp500-valuation-concentration"
    },
    {
      "dimension": "valuation-split",
      "metric": "june-2026-top10-minus-remaining-forward-pe",
      "label": "June 2026 top-10 minus remaining-company forward-P/E spread",
      "value": 2,
      "unit": "forward-pe",
      "asOfDate": "2026-06-30",
      "sourceStudySlug": "sp500-valuation-concentration",
      "sourceStudyPath": "/research/sp500-valuation-concentration"
    },
    {
      "dimension": "valuation-split",
      "metric": "forward-pe-spread-narrowing",
      "label": "March 2024 to June 2026 forward-P/E spread narrowing",
      "value": 8.1,
      "unit": "forward-pe",
      "asOfDate": "2026-06-30",
      "sourceStudySlug": "sp500-valuation-concentration",
      "sourceStudyPath": "/research/sp500-valuation-concentration"
    },
    {
      "dimension": "forward-return-sensitivity",
      "metric": "forward-return-observation-count",
      "label": "Non-overlapping 10-year forward-return observations",
      "value": 6,
      "unit": "count",
      "asOfDate": "2025-06-30",
      "sourceStudySlug": "sp500-concentration-forward-returns",
      "sourceStudyPath": "/research/sp500-concentration-forward-returns"
    },
    {
      "dimension": "forward-return-sensitivity",
      "metric": "starting-concentration-forward-return-correlation",
      "label": "Starting concentration vs subsequent 10-year return correlation",
      "value": -0.72,
      "unit": "correlation",
      "asOfDate": "2025-06-30",
      "sourceStudySlug": "sp500-concentration-forward-returns",
      "sourceStudyPath": "/research/sp500-concentration-forward-returns"
    },
    {
      "dimension": "forward-return-sensitivity",
      "metric": "correlation-excluding-1965",
      "label": "Correlation after excluding the June 1965 starting point",
      "value": -0.04,
      "unit": "correlation",
      "asOfDate": "2025-06-30",
      "sourceStudySlug": "sp500-concentration-forward-returns",
      "sourceStudyPath": "/research/sp500-concentration-forward-returns"
    },
    {
      "dimension": "forward-return-sensitivity",
      "metric": "leave-one-out-min-correlation",
      "label": "Most negative leave-one-out correlation",
      "value": -0.87,
      "unit": "correlation",
      "asOfDate": "2025-06-30",
      "sourceStudySlug": "sp500-concentration-forward-returns",
      "sourceStudyPath": "/research/sp500-concentration-forward-returns"
    }
  ],
  "methodology": {
    "derivationBoundary": "Every synthesis value is derived from one of the four published Grizzly Bulls S&P 500 concentration studies.",
    "dateBoundary": "The component studies use different data dates. The synthesis preserves each date rather than treating the series as one synchronized snapshot.",
    "denominatorBoundary": "Historical weight, trailing earnings share, forward P/E, and forward-return sensitivity use different denominators and should not be collapsed into a single score.",
    "refreshBoundary": "The series JSON and CSV are derived from the four published component study datasets, and every metric retains its source study and observation date."
  }
}