with the skill
**Two dates stand out: September 17 (0 signups) and September 25 (1,140 signups). Investigate them before dropping either.** The lower weekend counts look normal, not anomalous.
### Anomaly flags
| Date | Signups | Assessment | What to check |
|---|---:|---|---|
| **2026-09-17, Thu** | **0** | Other Thursdays recorded **329–344**. A zero is highly unusual. | Missing data, tracking failure, or a genuine signup/service outage. |
| **2026-09-25, Fri** | **1,140** | Other Fridays recorded **298–315**. This is about **3.7×** their average. | Campaigns, launches, bulk imports, duplicate events, or bot activity. |
**Normal pattern:** Aside from those two dates, weekdays range from **298–344**, while weekends range from **184–207**. That consistent weekly pattern means weekends should **not** be removed as low outliers. There is also a modest upward drift, especially on weekends, rather than another obvious isolated anomaly.
### Effect on your average
| Calculation | Daily mean | Daily median |
|---|---:|---:|
| All 28 days | **304.7** | **316** |
| Excluding both flagged days—sensitivity check only | **284.3** | **316** |
The two unusual values partly offset one another, so the overall mean alone hides them.
Show the rest (10 more lines)
### Recommendation before deleting anything
- **If the zero reflects a real outage:** keep it. It is part of actual signup performance.
- **If the zero means missing tracking:** recover the count if possible; otherwise mark it missing and disclose any estimation.
- **If the spike represents real signups:** keep it, even if a campaign caused it.
- **If the spike contains duplicates or invalid signups:** correct those records using a documented rule.
**Use the all-days mean for actual performance unless you establish a data-quality problem.** For “typical daily volume,” report the median alongside it and distinguish weekdays from weekends.
Also, this window is **September 7–October 4**, not a calendar month. If you mean September’s monthly average, you still need September 1–6 and should exclude October 1–4.