> ## 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 |


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