[Streams] Update data quality calculations

solutions/_snippets/failure-store-permissions.md

@@ -0,0 +1,6 @@
+To view and modify failure store in {{stack}}, you need the following data stream level privileges:
+
+* `read_failure_store`
+* `manage_failure_store`
+
+For more information, refer to [Granting privileges for data streams and aliases](../../deploy-manage/users-roles/cluster-or-deployment-auth/granting-privileges-for-data-streams-aliases.md).

solutions/observability/streams/management/data-quality.md

@@ -4,26 +4,41 @@ applies_to:
   stack: preview =9.1, ga 9.2+
 ---
 
-# Manage data quality [streams-data-retention]
+# Manage data quality [streams-data-quality]
 
-After selecting a stream, use the **Data quality** tab to find failed and degraded documents in your stream. Use the following components to monitor the health of your data and identify and fix issues:
+From the **Streams** page, use the **Data quality** menu to filter your streams by data quality status, then select a stream to examine it more closely. After selecting a stream, use the **Data quality** tab to find failed and degraded documents in your stream.
 
-- **Degraded documents:** Documents with the `ignored` property usually because of malformed fields or exceeding the limit of total fields when `ignore_above:false`. This component shows the total number of degraded documents, the percentage, and status (**Good**, **Degraded**, **Poor**).
-- **Failed documents:**: Documents that were rejected during ingestion because of mapping conflicts or pipeline failures.
-- **Quality score:** Streams calculates the overall quality score (**Good**, **Degraded**, **Poor**) based on the percentage of degraded and failed documents.
-- **Trends over time:** A time-series chart so you can track how degraded and failed documents are accumulating over time. Use the date picker to zoom into a specific range and understand when problems are spiking.
-- **Issues:** {applies_to}`stack: preview 9.2`Find issues with specific fields, how often they've occurred, and when they've occurred.
+Use the following components to monitor the health of your data and identify and fix issues:
 
-## Failure store
+* **Degraded documents:** Documents from the last backing index of the stream with the `ignored` property, usually because of malformed fields or fields with values that exceed the configured `ignore_above` limit. This component shows:
+  * Total number of degraded documents.
+  * Percentage of degraded documents relative to the total document count from the stream's last backing index.
+  * The data quality status (**Good**, **Degraded**, **Poor**).
+* **Failed documents:** Documents that were rejected during ingestion because of mapping conflicts or pipeline failures. This component shows:
+  * Total number of failed documents that correspond with this stream from within the specified time range in the date picker. Refer to [Failure store](#streams-data-quality-failure) for more information.
+  * Percentage of failed documents relative to the total document count from the stream's last backing index.
+  * The data quality status (**Good**, **Degraded**, **Poor**).
+* **Quality score:** Streams calculates the overall quality score (**Good**, **Degraded**, **Poor**) based on the percentage of degraded and failed documents. Refer to [Data quality calculation](#streams-data-quality-calculation) for more information.
+* **Trends over time:** A time-series chart so you can track how degraded and failed documents are accumulating over time. Use the date picker to focus on a specific range and understand when problems are spiking.
+* {applies_to}`stack: preview 9.2` **Issues:** Find issues with specific fields, how often they've occurred, and when they've occurred.
 
-A [failure store](../../../../manage-data/data-store/data-streams/failure-store.md) is a secondary set of indices inside a data stream, dedicated to storing failed documents. Instead of losing documents that are rejected during ingestion, a failure store retains it in a `::failures` index, so you can review failed documents to understand what went wrong and how to fix it.
+## Data quality calculation [streams-data-quality-calculation]
 
-### Required permissions
-To view and modify failure store in {{stack}}, you need the following data stream level privileges:
-- `read_failure_store`
-- `manage_failure_store`
+Streams calculates data quality as follows:
+
+* **Good:** Both the **Degraded documents** percentage and the **Failed documents** percentage are 0.
+* **Degraded:** Either the **Degraded documents** percentage or the **Failed documents** percentage are greater than 0 and less than or equal to 3.
+* **Poor:** Either the **Degraded documents** percentage or the **Failed documents** percentage are greater than 3.
+
+## Failure store [streams-data-quality-failure]
 
-For more information, refer to [Granting privileges for data streams and aliases](../../../../deploy-manage/users-roles/cluster-or-deployment-auth/granting-privileges-for-data-streams-aliases.md).
+A [failure store](../../../../manage-data/data-store/data-streams/failure-store.md) is a secondary set of indices inside a data stream, dedicated to storing failed documents. Instead of losing documents that are rejected during ingestion, a failure store retains them in a `::failures` index, so you can review failed documents to understand what went wrong and how to fix it.
+
+For example, for a stream called `my-stream`, Streams fetches all documents from the `my-stream::failures` index from within the specified time range in the date picker.
+
+### Required permissions
+:::{include} ../../../_snippets/failure-store-permissions.md
+:::
 
 ### Turn on failure stores
 In Streams, you need to turn on failure stores to get failed documents. To do this, select **Enable failure store** in the **Failed documents** component. From here you can set your failure store retention period.