{
  "alt": "Line chart by presidential election from 1992 to 2024 with a House line and a Senate line, each with an interval band. The House correlation is {fact:house_r_1992} in 1992, {fact:house_r_2008} in 2008, {fact:house_r_2012} in 2012 and {fact:house_r_2024} in 2024. The Senate correlation is {fact:senate_r_1992} in 1992 and {fact:senate_r_2024} in 2024.",
  "caption": "Both lines rise toward one, though not at every step, with the House line at {fact:house_r_2012} in 2012 and {fact:house_r_2024} in 2024. Each point is a correlation across the counties in the sample, weighted by presidential two-party votes. Bands are 95% intervals from a bootstrap that resamples whole states. The second view plots the average size of the gap between the two margins, in points.",
  "data": [
    {
      "conf_high": 0.721928,
      "conf_low": 0.557926,
      "estimate": 0.649108,
      "measure": "correlation",
      "n_units": 2735,
      "office": "House",
      "year": 1992
    },
    {
      "conf_high": 18.6893,
      "conf_low": 14.5457,
      "estimate": 16.3574,
      "measure": "gap",
      "n_units": 2735,
      "office": "House",
      "year": 1992
    },
    {
      "conf_high": 0.838815,
      "conf_low": 0.729813,
      "estimate": 0.793338,
      "measure": "correlation",
      "n_units": 2703,
      "office": "House",
      "year": 1996
    },
    {
      "conf_high": 18.3306,
      "conf_low": 14.9606,
      "estimate": 16.5336,
      "measure": "gap",
      "n_units": 2703,
      "office": "House",
      "year": 1996
    },
    {
      "conf_high": 0.800681,
      "conf_low": 0.656694,
      "estimate": 0.738804,
      "measure": "correlation",
      "n_units": 2555,
      "office": "House",
      "year": 2000
    },
    {
      "conf_high": 19.8895,
      "conf_low": 16.0465,
      "estimate": 17.9822,
      "measure": "gap",
      "n_units": 2555,
      "office": "House",
      "year": 2000
    },
    {
      "conf_high": 0.840518,
      "conf_low": 0.690903,
      "estimate": 0.778893,
      "measure": "correlation",
      "n_units": 2479,
      "office": "House",
      "year": 2004
    },
    {
      "conf_high": 17.675,
      "conf_low": 13.8211,
      "estimate": 15.6188,
      "measure": "gap",
      "n_units": 2479,
      "office": "House",
      "year": 2004
    },
    {
      "conf_high": 0.856504,
      "conf_low": 0.756094,
      "estimate": 0.817669,
      "measure": "correlation",
      "n_units": 2661,
      "office": "House",
      "year": 2008
    },
    {
      "conf_high": 15.2388,
      "conf_low": 12.0753,
      "estimate": 13.4908,
      "measure": "gap",
      "n_units": 2661,
      "office": "House",
      "year": 2008
    },
    {
      "conf_high": 0.960876,
      "conf_low": 0.934806,
      "estimate": 0.949844,
      "measure": "correlation",
      "n_units": 2609,
      "office": "House",
      "year": 2012
    },
    {
      "conf_high": 8.52593,
      "conf_low": 6.78918,
      "estimate": 7.62747,
      "measure": "gap",
      "n_units": 2609,
      "office": "House",
      "year": 2012
    },
    {
      "conf_high": 0.958127,
      "conf_low": 0.894925,
      "estimate": 0.932764,
      "measure": "correlation",
      "n_units": 2427,
      "office": "House",
      "year": 2016
    },
    {
      "conf_high": 10.0125,
      "conf_low": 7.57681,
      "estimate": 8.72806,
      "measure": "gap",
      "n_units": 2427,
      "office": "House",
      "year": 2016
    },
    {
      "conf_high": 0.990878,
      "conf_low": 0.984246,
      "estimate": 0.987941,
      "measure": "correlation",
      "n_units": 2884,
      "office": "House",
      "year": 2020
    },
    {
      "conf_high": 4.90559,
      "conf_low": 3.7686,
      "estimate": 4.31906,
      "measure": "gap",
      "n_units": 2884,
      "office": "House",
      "year": 2020
    },
    {
      "conf_high": 0.992078,
      "conf_low": 0.987288,
      "estimate": 0.989664,
      "measure": "correlation",
      "n_units": 2695,
      "office": "House",
      "year": 2024
    },
    {
      "conf_high": 4.21731,
      "conf_low": 3.23518,
      "estimate": 3.69775,
      "measure": "gap",
      "n_units": 2695,
      "office": "House",
      "year": 2024
    },
    {
      "conf_high": 0.794413,
      "conf_low": 0.473779,
      "estimate": 0.631349,
      "measure": "correlation",
      "n_units": 1824,
      "office": "Senate",
      "year": 1992
    },
    {
      "conf_high": 21.0888,
      "conf_low": 12.1202,
      "estimate": 15.9327,
      "measure": "gap",
      "n_units": 1824,
      "office": "Senate",
      "year": 1992
    },
    {
      "conf_high": 0.912109,
      "conf_low": 0.760153,
      "estimate": 0.841437,
      "measure": "correlation",
      "n_units": 2288,
      "office": "Senate",
      "year": 1996
    },
    {
      "conf_high": 14.9639,
      "conf_low": 7.78017,
      "estimate": 10.8891,
      "measure": "gap",
      "n_units": 2288,
      "office": "Senate",
      "year": 1996
    },
    {
      "conf_high": 0.88054,
      "conf_low": 0.724453,
      "estimate": 0.815539,
      "measure": "correlation",
      "n_units": 1858,
      "office": "Senate",
      "year": 2000
    },
    {
      "conf_high": 18.4514,
      "conf_low": 10.7819,
      "estimate": 13.893,
      "measure": "gap",
      "n_units": 1858,
      "office": "Senate",
      "year": 2000
    },
    {
      "conf_high": 0.86967,
      "conf_low": 0.66612,
      "estimate": 0.782166,
      "measure": "correlation",
      "n_units": 2006,
      "office": "Senate",
      "year": 2004
    },
    {
      "conf_high": 23.3758,
      "conf_low": 13.5133,
      "estimate": 18.0463,
      "measure": "gap",
      "n_units": 2006,
      "office": "Senate",
      "year": 2004
    },
    {
      "conf_high": 0.924419,
      "conf_low": 0.801743,
      "estimate": 0.874861,
      "measure": "correlation",
      "n_units": 2055,
      "office": "Senate",
      "year": 2008
    },
    {
      "conf_high": 15.7727,
      "conf_low": 8.82398,
      "estimate": 12.0602,
      "measure": "gap",
      "n_units": 2055,
      "office": "Senate",
      "year": 2008
    },
    {
      "conf_high": 0.9655,
      "conf_low": 0.877237,
      "estimate": 0.932134,
      "measure": "correlation",
      "n_units": 1843,
      "office": "Senate",
      "year": 2012
    },
    {
      "conf_high": 12.5032,
      "conf_low": 5.65822,
      "estimate": 8.70569,
      "measure": "gap",
      "n_units": 1843,
      "office": "Senate",
      "year": 2012
    },
    {
      "conf_high": 0.962064,
      "conf_low": 0.906507,
      "estimate": 0.928391,
      "measure": "correlation",
      "n_units": 1989,
      "office": "Senate",
      "year": 2016
    },
    {
      "conf_high": 13.0428,
      "conf_low": 7.72204,
      "estimate": 10.1108,
      "measure": "gap",
      "n_units": 1989,
      "office": "Senate",
      "year": 2016
    },
    {
      "conf_high": 0.993322,
      "conf_low": 0.977397,
      "estimate": 0.987693,
      "measure": "correlation",
      "n_units": 2212,
      "office": "Senate",
      "year": 2020
    },
    {
      "conf_high": 4.90495,
      "conf_low": 3.2443,
      "estimate": 3.93013,
      "measure": "gap",
      "n_units": 2212,
      "office": "Senate",
      "year": 2020
    },
    {
      "conf_high": 0.990743,
      "conf_low": 0.969075,
      "estimate": 0.982126,
      "measure": "correlation",
      "n_units": 1749,
      "office": "Senate",
      "year": 2024
    },
    {
      "conf_high": 6.03673,
      "conf_low": 3.4448,
      "estimate": 4.57016,
      "measure": "gap",
      "n_units": 1749,
      "office": "Senate",
      "year": 2024
    }
  ],
  "id": "margin_tracking",
  "notes": [
    "County returns are full counts. The intervals show how much the correlation depends on which states are in the sample: whole states are resampled in a bootstrap, and the methods note gives the replicates and seed.",
    "The gap view plots the vote-weighted mean absolute difference between the down-ballot margin and the presidential margin, in points of margin."
  ],
  "source": "County returns for President, U.S. House and U.S. Senate, 1992-2024 (Heideman 2026, with MIT Election Data and Science Lab presidential returns); full counts, unweighted",
  "spec": {
    "colors": {
      "House": "cat1",
      "Senate": "cat2"
    },
    "dashed": [
      "Senate"
    ],
    "hi": "conf_high",
    "lo": "conf_low",
    "n": "n_units",
    "series": "office",
    "x": "year",
    "xDomain": [
      1990,
      2026
    ],
    "xLabel": "Presidential election",
    "xTicks": [
      1992,
      1996,
      2000,
      2004,
      2008,
      2012,
      2016,
      2020,
      2024
    ],
    "y": "estimate",
    "yDomain": [
      0.3,
      1
    ],
    "yFormat": {
      "digits": 2
    },
    "yLabel": "Correlation of county margins"
  },
  "subtitle": "Vote-weighted correlation across counties between the Democratic minus Republican margin for president and for the House (or Senate), counties in contested races, 1992 to 2024; 95% intervals",
  "table": {
    "columns": [
      {
        "key": "office",
        "label": "Office"
      },
      {
        "key": "measure",
        "label": "Measure"
      },
      {
        "key": "year",
        "label": "Election"
      },
      {
        "format": {
          "digits": 2
        },
        "key": "estimate",
        "label": "Estimate"
      },
      {
        "format": {
          "digits": 2
        },
        "key": "conf_low",
        "label": "Lower"
      },
      {
        "format": {
          "digits": 2
        },
        "key": "conf_high",
        "label": "Upper"
      },
      {
        "format": {
          "thousands": true
        },
        "key": "n_units",
        "label": "Counties"
      }
    ]
  },
  "title": "The correlation between county presidential and House margins rose from {fact:house_r_1992} in 1992 to {fact:house_r_2024} in 2024",
  "type": "line",
  "views": [
    {
      "filter": {
        "measure": "correlation"
      },
      "id": "correlation",
      "label": "Correlation"
    },
    {
      "caption": "The vote-weighted average absolute gap between the two margins was {fact:house_mad_1992} points in 1992 and {fact:house_mad_2024} points in 2024 for the House, and {fact:senate_mad_1992} and {fact:senate_mad_2024} points for the Senate. Bands are 95% intervals from a bootstrap that resamples whole states.",
      "filter": {
        "measure": "gap"
      },
      "id": "gap",
      "label": "Average gap in points",
      "spec": {
        "yDomain": [
          0,
          30
        ],
        "yFormat": {
          "digits": 0
        },
        "yLabel": "Average absolute gap (points of margin)"
      },
      "title": "The average gap between county House and presidential margins fell from {fact:house_mad_1992} points in 1992 to {fact:house_mad_2024} points in 2024"
    }
  ],
  "width": "wide"
}