> ## Documentation Index
> Fetch the complete documentation index at: https://docs.upstackdata.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Affected Events %: Share of Events with Quality Issues

> Track the percentage of events impacted by a specific diagnostic issue. Identify which issues affect the most events to prioritize fixes.

<Tip>
  The share of your total events impacted by a specific diagnostic issue.
</Tip>

## Formula

<Info>
  **Affected Events %** = [**Affected Event Count**](/reference/metrics/data-quality/emq/affected-event-count) ÷ **Total Events** × 100
</Info>

### Formula Components

| Metric                                                                               | Definition                                         |
| ------------------------------------------------------------------------------------ | -------------------------------------------------- |
| [**Affected Event Count**](/reference/metrics/data-quality/emq/affected-event-count) | Number of events impacted by this diagnostic issue |
| **Total Events**                                                                     | Total number of events sent during the period      |

| Metadata        |                                   |
| --------------- | --------------------------------- |
| **Type**        | Percentage                        |
| **Data Source** | [Meta Ads](/sources/facebook-ads) |
| **Aggregation** | Average                           |

***

## Example

Your pixel has **3 active diagnostics**. Here's how they affect your events:

| Diagnostic Issue     | Affected % | Priority |
| -------------------- | ---------- | -------- |
| Missing email hash   | 42.3%      | High     |
| Invalid phone format | 8.7%       | Medium   |
| Missing external\_id | 2.1%       | Low      |

The "Missing email hash" issue impacts 42.3% of your events and should be fixed first.

***

## How It Works

Meta analyzes your event data and flags quality issues that reduce matching accuracy. Affected Events % shows what portion of your total event volume is impacted by each specific issue. Higher percentages indicate issues affecting more of your data.

***

## When to Use

| Scenario              | Action                                           |
| --------------------- | ------------------------------------------------ |
| Prioritizing fixes    | Address issues with the highest affected % first |
| Measuring fix impact  | Compare before/after to confirm resolution       |
| Tracking data quality | Monitor trends over time for quality regressions |
| Resource allocation   | Focus engineering time on highest-impact issues  |

***

## Related Metrics

| Metric                                                                           | Relationship                                                |
| -------------------------------------------------------------------------------- | ----------------------------------------------------------- |
| [Affected Event Count](/reference/metrics/data-quality/emq/affected-event-count) | Absolute count of events (this metric shows the percentage) |
| [Diagnostics Count](/reference/metrics/data-quality/emq/diagnostics-count)       | Total number of active diagnostic issues                    |
| [EMQ Score](/reference/metrics/data-quality/emq/emq-score)                       | Overall quality score impacted by these issues              |

[See all EMQ metrics →](/reference/metrics/data-quality/emq)