Abstract: A method to facilitate consumer behavioral research from end users. When necessary to find sufficiently qualified respondents to meet an audience segment to be surveyed, mobile devices that are or have been in a location of interest are identified (e.g., by their device identifiers). With respect to any device identifier that matches a device identifier in first party data, a query is issued to third party data sources (e.g., advertising networks, exchanges, etc.) to obtain information that the data sources possess with respect to an end user associated with that identifier. As responses to the queries are received, they are filtered against a probability sample, which represents a set of respondents having demographic attributes consistent with the audience segment, to determine whether an end user (e.g., present in-location) should be included in a set of respondents. If so, an end user experience opportunity (e.g., a survey) is issued to the mobile device.