There is not a set minimum number of participants that we would recommend to complete the IDI in order to get a clear picture of your organization's level of intercultural competence. Because an organization or group is made up of people, to get the most accurate understanding of the organization, ideally you would administer the IDI to as many individuals as possible. However, we understand that this is not always possible due to lack of resources.
One alternative option is to start with all members of leadership teams. This would not be representative of the organization as a whole, but would represent those who likely have the most influence, make policies, etc., and can provide useful information.
If you opt to do a sample of the organization, you should think carefully about how you select the individuals who are asked to/allowed to participate, and what implications that might have on others in the organization who do not have the same opportunity. IDI, LLC does not have guidelines on sampling; we recommend that you contact a statistician.