{
  "slug": "conversion-rate-change",
  "name": "Conversion-rate change",
  "aliases": [
    "Conversion rate delta",
    "Conversion rate period over period"
  ],
  "definition": "The difference between a period's conversion rate and a comparison period's, reported alongside both rates and their underlying counts.",
  "category": "Statistics",
  "type": "derived metric",
  "unit": "difference between two rates, on whatever scale the underlying rate measure carries, rounded to two decimal places",
  "direction": "higher-better",
  "verification": "verified",
  "calculation": "The rate under test is the product's OWN displayed conversion-rate measure, conversions divided by unique users, or, on tenants whose analytics supply a stored per-row rate, the average of those stored rates. Both periods' rates are fetched as the product's weighted period aggregates and the change is the selected rate minus the comparison rate, rounded to two decimal places. A relative form is reported beside it as a percentage to two decimal places. Both period rates are echoed in the response so the subtraction is checkable.",
  "numerator": "Selected-period rate minus comparison-period rate",
  "denominator": "Each rate's own denominator is set by the underlying measure: unique users, or none at all where the measure is an average of stored per-row rates",
  "aggregation": "Computed once from the two periods' weighted aggregates, not averaged over buckets, the per-bucket series exists but is used for the significance test, not for the change.",
  "grain": "One value per pair of date ranges.",
  "dimensions": [],
  "requiredFilters": [
    "date_range",
    "comparison_range"
  ],
  "sources": [
    "web-analytics"
  ],
  "reports": [
    "ai-referral-traffic-report",
    "search-to-revenue-report"
  ],
  "skills": [
    "significance-referee",
    "anomaly-investigator",
    "search-to-revenue"
  ],
  "verbs": [
    "pop_significance"
  ],
  "rungs": [
    "R5"
  ],
  "levers": [],
  "questions": [
    "Did conversion rate really change versus last month?",
    "How much did conversion rate move?"
  ],
  "interpretation": "The size of the move, kept separate from whether the move is distinguishable from noise. Read it beside the p-value and the verdict: a large change on thin traffic and a small change on heavy traffic can carry the same p-value, and only the pair tells the story. Because it is the difference between the two numbers the product itself displays, it should reconcile against the product UI exactly, which is the point of it.",
  "caveats": [
    "The change and the significance test are computed on DIFFERENT quantities. The change is the difference between two weighted period aggregates; the test compares equal-weight per-bucket means. When traffic weights shift between periods those two can move in opposite directions, and when they do the tool refuses to transfer the verdict, it returns a can't-tell for the displayed rate and withholds the significance flag rather than making a claim about a quantity the test did not measure.",
    "The denominator is not sessions. It is unique users, or, on tenants whose analytics supply a stored per-row rate, no explicit denominator at all, the measure is an average of stored rates. A change computed against a session-based rate will not match this one.",
    "It is a difference between two rates, not a percentage-point figure and not a percent change, the relative form is a separate field with its own scale problem.",
    "Fewer than two buckets in either period, or no within-period variation, returns a can't-tell with an explanatory note; the aggregate change is still reported, because it was already known before the test was attempted.",
    "Whole-domain only; a non-default segment returns a note explaining the limitation.",
    "The result is stamped observational in the payload."
  ],
  "freshness": "loads nightly, a same-day question gets yesterday's number, labelled as yesterday's.",
  "failureModes": [
    "Reconstructing the rate as conversions over sessions and comparing the two.",
    "Reading the value as percentage points.",
    "Presenting a significance verdict for the displayed change when the tool withheld one because the two quantities disagreed in direction.",
    "Quoting the change without the verdict beside it."
  ],
  "notSameAs": [
    {
      "slug": "conversion-rate",
      "why": "One is a level for a single period; the other is the difference between two of those levels. They share a definition and a denominator, what differs is the question, and the fact that only the change carries a significance verdict."
    },
    {
      "slug": "rate-change-percent",
      "why": "One is an absolute difference between two rates, in percentage points; the other expresses that difference relative to the comparison period. Confirm which you have before quoting it, they answer different questions and are not interchangeable."
    }
  ],
  "related": [
    "conversion-rate",
    "rate-change-percent",
    "significance-p-value",
    "real-noise-verdict"
  ],
  "workflows": [],
  "lastVerified": "2026-08-04"
}