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

# Master control group history

Master control group (MCG) is an established tool for excluding parts of the contact database from all communication over a period of time. Usually the purpose of exclusion with master control group is to measure the effect of marketing activities over periods of time.

| **Field**              | **Description**                                     | **Data type** | **Example value**                    |
| :--------------------- | :-------------------------------------------------- | :------------ | :----------------------------------- |
| contactId              | The unique contact ID                               | GUID          | a72d5017-827c-40dd-8585-abc90086e0ac |
| startDateTime          | When the contact was put in the control group       | datetime      | 2020-06-28T21:59:59+01:00            |
| endDateTime            | When the contact was taken out of the control group | datetime      | 2020-07-28T21:59:59+01:00            |
| isInMasterControlGroup | If a contact is in this control group               | boolean       | true                                 |
| changeType             | Not applicable                                      | string        | CREATE/UPDATE/DELETE                 |