{
  "slug": "pop-delta",
  "name": "Period-over-period change",
  "aliases": [
    "Delta",
    "PoP change",
    "Change vs prior period"
  ],
  "definition": "The difference between a metric in the selected period and the same metric in a comparison period, computed from two identical queries that differ only in their date filter.",
  "category": "Search performance",
  "type": "derived metric",
  "unit": "the same unit as the metric being compared",
  "direction": "neutral",
  "verification": "verified",
  "calculation": "delta = selected − comparison. Each side is rounded to two decimals before the subtraction; either side missing yields null rather than zero. The comparison leg is the selected leg's query with only the period filter value swapped, so every other filter is held identical.",
  "aggregation": "Computed per row and joined on the row key, the non-numeric columns of the result, never on row order, because the two periods return different key sets at page and query grain. Rows present in only one of the two periods get a null delta, not a delta against zero; only their counts are reported. Row-index pairing survives in exactly one place: a pure aggregate with no dimension columns, where both sides are a single row.",
  "grain": "One row key × the pair of periods.",
  "dimensions": [
    "query",
    "page",
    "country",
    "device",
    "intent",
    "category"
  ],
  "requiredFilters": [
    "date range",
    "comparison range"
  ],
  "sources": [
    "search-console"
  ],
  "reports": [
    "ai-overview-report",
    "cannibalization-report",
    "content-decay-report",
    "content-performance-report",
    "crawl-log-report",
    "keyword-ranking-report",
    "monthly-executive-search-report",
    "serp-volatility-report",
    "weekly-search-report"
  ],
  "skills": [
    "weekly-search-report",
    "rank-movement-review",
    "anomaly-investigator",
    "content-decay-refresh"
  ],
  "verbs": [
    "compare_periods",
    "search_performance",
    "gsc_breakdown",
    "seo_ranking_movement_report"
  ],
  "rungs": [
    "R2",
    "R5"
  ],
  "levers": [],
  "questions": [
    "How did clicks change versus the previous month?",
    "Compare last week to the week before by page",
    "Which categories lost the most impressions versus last quarter?"
  ],
  "interpretation": "A description of what changed, not a claim that it changed for a reason or that the change is distinguishable from noise. Comparisons hold every filter constant except the date, so a delta is only as like-for-like as the two windows are, unequal lengths, or a window that straddles a seasonal break, produce a real delta about the wrong thing.",
  "caveats": [
    "The comparison window is explicit; the assistant does date arithmetic rather than relying on relative expressions, so a mis-specified window silently produces a valid delta about the wrong period.",
    "Unmatched rows are counted and reported separately, and their delta is null rather than a number. Reading the unmatched count itself as a set of launches and collapses is the common misread, it is a coverage difference between two windows.",
    "Position deltas invert: a negative delta is an improvement."
  ],
  "freshness": "1 to 2 days behind, Google's own reporting lag. Any answer touching the last 48 hours says so on the card.",
  "failureModes": [
    "Comparing a 28-day window to a calendar month and reading the length difference as performance.",
    "Substituting zero for an unmatched row's null delta and totalling it into a period change."
  ],
  "notSameAs": [
    {
      "slug": "real-noise-verdict",
      "why": "A delta states how far the number moved; a significance verdict states whether the move is distinguishable from noise at an alpha. The verdict is a p-value threshold only, no effect size is computed anywhere, so a significant change can be trivially small and a large delta can fail the test."
    }
  ],
  "related": [
    "pop-delta-pct",
    "ranking-movement",
    "clicks"
  ],
  "workflows": [],
  "lastVerified": "2026-08-04"
}