Consider two different meanings of “double survey.” One meaning applies to a law firm sending out two surveys, each to a different target audience, and then combining the responses in a report. A second meaning applies to a firm conducting more than one survey in a year, but with the same target audience.
Burgess Salmon Infrastructure 2018 [pg. 8] explains that it simultaneously conducted two separate surveys, one by interviews and the other by an online questionnaire. The report juxtaposes the findings.
Minter Ellison Cybersecurity 2017 [pg. 6] also undertook a double survey. With separate instruments, it reached out to members of boards of directors and also to chief information officers and others. The report combines the data.
Turning to the second meaning of “double survey”, one example started in 2015. Haynes Boone has conducted its energy borrowing survey twice yearly since then, e.g., Haynes Boone Borrowing 2018 [pg. 2].
Other firms that have conducted surveys twice a year on a topic include Morrison Foerster, e.g., Morrison Foerster MA 2018, and Irwin Mitchell, e.g., Irwin Mitchell Occupiers 2014. We also found an instance of quarterly surveys: Brodies Firm Brexit 2017!