GA4 weekly anomaly report: week of Oct 19 (Oct 19 to Oct 25)
Data: your fictional export (run 2026-10-29, v0.3.0), weeks labeled by Monday start date. All five weeks (Sep 21 to Oct 19) are complete; Oct 25 is before today (Oct 29). Key event: purchase. Threshold: more than 15 percent beyond the prior four week range.
1. Summary
- Organic Search purchases fell to 120 and revenue to $7,200, both about 24 percent below the prior four week low, while organic sessions were normal (8,050).
- The drop sits entirely on the homepage (/): 40 purchases vs 78 to 85 before; /products held at 80. The new homepage hero launched Oct 20, inside this week.
- Paid Search sessions jumped to 4,400 (41.9 percent above the prior high) with purchases and revenue flat.
2. Anomaly table
Per-week totals (sum of the export rows for each week; prior weeks Sep 21 to Oct 12, this week Oct 19):
| Metric | Segment | Sep 21 | Sep 28 | Oct 05 | Oct 12 | Oct 19 (this week) |
|---|---|---|---|---|---|---|
| Sessions | Total | 11,000 | 11,300 | 10,850 | 11,150 | 12,450 |
| Purchases | Total | 250 | 265 | 246 | 257 | 216 |
| Revenue | Total | $15,000 | $15,900 | $14,760 | $15,420 | $12,960 |
| Sessions | Organic Search | 8,000 | 8,200 | 7,900 | 8,100 | 8,050 |
| Purchases | Organic Search | 160 | 170 | 158 | 165 | 120 |
| Revenue | Organic Search | $9,600 | $10,200 | $9,480 | $9,900 | $7,200 |
| Sessions | Paid Search | 3,000 | 3,100 | 2,950 | 3,050 | 4,400 |
| Purchases | Paid Search | 90 | 95 | 88 | 92 | 96 |
| Revenue | Paid Search | $5,400 | $5,700 | $5,280 | $5,520 | $5,760 |
Prior range rule: min is the smallest and max the largest of the four prior weekly values in the row above; mean is their sum divided by four.
| Metric | Segment | This week | Prior 4 weeks (min to max) | Prior mean | Beyond range | Flag |
|---|---|---|---|---|---|---|
| Purchases | Organic Search | 120 | 158 to 170 | 163.25 | -24.1% | Anomaly |
| Revenue | Organic Search | $7,200 | $9,480 to $10,200 | $9,795 | -24.1% | Anomaly |
| Sessions | Paid Search | 4,400 | 2,950 to 3,100 | 3,025 | +41.9% | Anomaly |
| Sessions | Organic Search | 8,050 | 7,900 to 8,200 | 8,050 | in range | No |
| Purchases | Paid Search | 96 | 88 to 95 | 91.25 | +1.1% | No (noise) |
| Revenue | Paid Search | $5,760 | $5,280 to $5,700 | $5,475 | +1.1% | No (noise) |
| Sessions | Total | 12,450 | 10,850 to 11,300 | 11,075 | +10.2% | No |
| Purchases | Total | 216 | 246 to 265 | 254.5 | -12.2% | No |
| Revenue | Total | $12,960 | $14,760 to $15,900 | $15,270 | -12.2% | No |
Beyond range = distance past the nearest bound, divided by that bound.
3. Drill down
| Segment | Landing page | Sessions this week (prior range) | Purchases this week (prior range) | Revenue this week (prior range) |
|---|---|---|---|---|
| Organic Search | / | 4,000 (3,950 to 4,100) | 40 (78 to 85), -48.7% | $2,400 ($4,680 to $5,100), -48.7% |
| Organic Search | /products | 4,050 (3,950 to 4,100) | 80 (80 to 85), in range | $4,800 ($4,800 to $5,100), in range |
| Paid Search | /sale | 4,400 (2,950 to 3,100), +41.9% | 96 (88 to 95) | $5,760 ($5,280 to $5,700) |
The organic loss is concentrated on the homepage: its purchase rate fell to 1.0 percent from 1.97 to 2.07 percent, on normal traffic. Paid Search has one landing page, so the spike cannot be narrowed further; its purchase rate fell to 2.18 percent from 2.98 to 3.06 percent.
4. Hypotheses to check
None of these is a confirmed cause. 1. Tracking change: a purchase tag change on the homepage path. For: the drop is on one page only. Against: /products and Paid purchases tracked normally. Check tag changes since Oct 19. 2. Known change, homepage hero (Oct 20): for: same week and same page as the drop. Against: nothing in the data yet links them; the hero went live a day into the week. Check homepage purchases by day and the click path from the hero. 3. Campaign start or stop: the Paid sessions spike with flat purchases fits added or broader paid traffic to /sale. Check paid campaigns, budgets and targeting for Oct 19 week. 4. Seasonality: no prior year data in the export; compare the same week last year. 5. Site issue: check the homepage for broken links or checkout errors since Oct 19.
5. Questions
- Did anyone change tags, the purchase event or checkout in the week of Oct 19?
- Where does the new hero send visitors, and did that link change?
- Did any paid campaign to /sale launch, expand or change budget that week?
- Can you share last year's same weeks for a seasonality check?
Needs your decision
- Approve before this report is sent to anyone beyond you. It has not been sent.