# Spike in GA4 Traffic

In the last week of September 2023, Google Merch store saw unusually high traffic spike.

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1696475932731/1ebb5f10-0357-48e7-a234-48da2904596e.png align="center")

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1696476383568/12bb9426-2a6d-4938-a8d5-a60e740d50b2.png align="center")

# **Investigate a spike in your data**

Some pointers

1. **Is this metric important?**
    
2. **Is the spike just a natural variation?**
    
3. **Consider seasonal trends and natural cycles**
    
4. **Is there a data quality issue?**
    
5. **Segment the data, follow the breadcrumbs**
    
6. **Have we changed anything internally?**
    

## Anomaly detection in Google Analytics 4

[This article](https://support.google.com/analytics/answer/9517187) discusses what anomaly detection is and how it works. It also details the 2 methods uses to identify anomalies over several metrics and dimension values.:

* time-series based anomaly detection
    
* anomaly detection simultaneously
    

Important points from this article are that the training period for *hourly* anomalies is **2 weeks**, the training period for *daily* anomalies is **90 days**, and the training period for *weekly* anomalies is **32 weeks**.

Additionally, if any particular segment demonstrates anomalous behavior across any metric and comprises at least 0.05% of the users on that property, it will be surfaced as an anomaly.

## Drilling Down

Anniversary-related mementos are the most purchased items.

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1696476736698/1f2d64e0-a500-45ee-9842-2466cffc3445.png align="center")

This spike is the result of Google 25th Anniversary. (1998 - 2023)

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1696477098708/e0fa2616-03bc-41c1-bfbb-4b95ad8eb352.jpeg align="center")