# Time-dependent Cohort Summary Statistics in Atlas

The Atlas **Characterizations** option allows you to create **cohort-level descriptive summary statistics.**

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Time-dependent statistics (e.g. *Demographics Age*) are based on the first time a person enters the cohort. This time is defined using **Cohort Entry Events** when creating a cohort in **Cohort Definitions**.
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In some cases (e.g. GWAS), cohorts can be created either using **Inclusion Criteria** or **Cohort Entry Events** in **Cohort Definitions.** However, cohorts for time-dependent summary statistics in **Characterizations** must be created using **Cohort Entry Events.**
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### **Correct time-dependent summary statistics using Cohort Entry Events**

Below, we have defined a cases cohort for e\_xcessive earwax\_ using **Cohort Entry Events*****.*** The first time a person enters this cohort is when e\_xcessive earwax\_ is diagnosed for the first time in a person’s life.

![](https://3072695768-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MhYL0UTLjqsuIdK0SSO%2Fuploads%2Fgit-blob-0376e7699dc55014b7f2312c335908a939b5fe57%2Fimage%20\(292\).png?alt=media)

We have also defined a controls cohort using **Cohort Entry Events*****.*** The first time a person enters this cohort is the earliest time when they have any health record (**Any Visit**) in FinnGen.

![](https://3072695768-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MhYL0UTLjqsuIdK0SSO%2Fuploads%2Fgit-blob-0a70aabe4b1259c17e708e1df37144b42154ec46%2Fimage%20\(418\).png?alt=media)

In **Characterizations,** the cases cohort will have the blue age distribution plot showing that the first time a person is diagnosed with e\_xcessive earwax\_ is usually between 60 and 85 years with an average age of 65 years. The controls cohort will have a much younger age distribution with an average age of 25 years.

![](https://3072695768-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MhYL0UTLjqsuIdK0SSO%2Fuploads%2Fgit-blob-998e926cbfb277e8e5d36ead088498cf6d84da1f%2Fimage%20\(270\).png?alt=media)

### **Incorrect time-dependent summary statistics using** Inclusion Criteria

The summary statistics will change if we define the cases cohort using **Inclusion Criteria** after first adding all persons into the cohort using **Cohort Entry Events**.

![](https://3072695768-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MhYL0UTLjqsuIdK0SSO%2Fuploads%2Fgit-blob-4e9e389c52d2dcbc9df0793427fbe5bc80c4e290%2Fimage%20\(229\).png?alt=media)

With the settings above, the summary statistics for the cases cohort is also based on the first time a person has any health record in FinnGen. **The summary statistics no longer show the time of the first excessive earwax diagnosis**.

![](https://3072695768-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MhYL0UTLjqsuIdK0SSO%2Fuploads%2Fgit-blob-3c72fddc7ea20dfb3702773e0f177a3a5aa4ed01%2Fimage%20\(461\).png?alt=media)

### Summary

* Time-dependent summary statistics (e.g. *Demographics Age*) depend on **Cohort Entry Events** to correctly define when a person enters the cohort
* Cohorts for summary statistics that are not time-dependent (e.g. *Demographics Gender)* can be defined either using **Cohort Entry Events** or **Inclusion Criteria**