# Time-dependent Cohort Summary Statistics in Atlas

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

{% hint style="info" %}
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**.
{% endhint %}

{% hint style="warning" %}
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.

![](/files/5pRnJ0XWHaKXLUrXrfjf)

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.

![](/files/UxBhSKdMUOBBlz6Jsdcr)

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.

![](/files/piSi3Nq9vZbWCZHEcwrX)

### **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**.

![](/files/XNXJK87JqkLeHxksiit6)

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**.

![](/files/OSjIxGp11Kd0taXHfLV9)

### 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**


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