Any sampled housing unit to which access by a data collector is physically blocked or impeded is considered to be a situation of controlled access. Impediments may include people (e.g. a "gatekeeper"), structures, and/or animals. Controlled access situations are encountered only in studies using the in-person field data collection methodology. Dealing effectively with these impediments is necessary to further the objectives of a field data collection operation.

Controlled access situations can take many forms and may involve one impediment or multiple impediments occurring simultaneously. For example, a single-family home may be surrounded by a locked fence or may have a growling dog loose in the yard, or both. A secured apartment building may have a locked entrance, a security guard, or both. An entire residential neighborhood ...