{
  "slug": "cwv-grade-distribution",
  "name": "Vital grade distribution",
  "aliases": [
    "Grade spread",
    "Pages by band"
  ],
  "definition": "How many of your pages fall into each grade band for a given vital.",
  "category": "Page experience",
  "type": "derived metric",
  "unit": "page counts per band",
  "direction": "neutral",
  "verification": "verified",
  "calculation": "Every page row's raw value for the vital is graded individually and tallied into the three bands. Rows with a non-numeric value are excluded from the tally rather than counted as poor.",
  "aggregation": "Counts of pages, not of measurements. The three counts add to the number of pages with a numeric value for that vital, which can be fewer than the total page count.",
  "grain": "Three counts per vital per date range, optionally per device.",
  "dimensions": [
    "page",
    "device"
  ],
  "requiredFilters": [
    "date_range"
  ],
  "sources": [
    "lighthouse"
  ],
  "reports": [
    "core-web-vitals-report"
  ],
  "skills": [
    "cwv-regression-watch",
    "technical-health-audit"
  ],
  "verbs": [
    "site_health_cwv_check"
  ],
  "rungs": [
    "R1"
  ],
  "levers": [
    "L1"
  ],
  "questions": [
    "How many pages fail LCP?",
    "Is the problem site-wide or a handful of pages?"
  ],
  "interpretation": "The shape behind the headline. A good weighted average with a heavy poor bucket is a template problem on a minority of pages; a middling average with everything bunched in the middle band is a site-wide one. The two call for different work, and only the distribution tells them apart.",
  "caveats": [
    "The page rows are capped, so the distribution describes the pages that were read, not every page on the site. A response that lands exactly on the cap says so, and must not then be described as covering the whole site.",
    "The distribution is built from per-page values while the headline grade is built from the product's summary measure, the two can disagree, and that disagreement is informative rather than a defect.",
    "With results split by device the rows are page-by-device observations rather than pages, so the band counts count measurements, not pages.",
    "Pages without a numeric value for a vital are excluded from its tally, so the three bands can sum to different totals across vitals.",
    "Collection cadence varies by page, so a distribution mixes measurements taken at different times."
  ],
  "freshness": "varies by site, priority URLs can run nightly; most pages far less often. The collection date rides on the card rather than being assumed.",
  "failureModes": [
    "Reading the band counts as a share of all site pages.",
    "Expecting the distribution's modal band to match the headline grade."
  ],
  "notSameAs": [
    {
      "slug": "cwv-vital-grade",
      "why": "One grade describes one value; the distribution describes how the pages spread across bands. A site graded good can still have a large poor bucket."
    }
  ],
  "related": [
    "cwv-vital-grade",
    "cwv-weakest-vital"
  ],
  "workflows": [],
  "lastVerified": "2026-08-04"
}