As mentioned in section 3.4.2 of the EC Guidance document on Monitoring and Evaluation, ensuring representativeness also for the regional dimension of the output indicators is considered as a good practice, but it is not a requirement. Regional representativeness could be achieved by establishing the sample one NUTS level lower than the level of the programme area (i.e. category of region). For instance, in the case of an Operational Programme at NUTS 2 level the sample would have the same distribution by NUTS 3 region as observed amongst all participants (see also section 4.4.1 of Annex D).