Impact of privacy legislation on the number and characteristics of people who are recruited for research: a randomised controlled trial

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Privacy laws have recently created restrictions on how researchers can approach study participants.


In a randomised trial of 152 patients, 50–74 years old, in a family practice, 60 were randomly selected to opt-out and 92 to opt-in methods. Patients were sent an introductory letter by their doctor in two phases, opt-out before and opt-in after introduction of the new Privacy Legislation in December 2001. Opt-out patients were contacted by researchers. Opt-in patients were contacted if patients responded by email, free telephone number or a reply-paid card.


Opt-in recruited fewer patients (47%; 43/92) after invitation compared with opt-out (67%; 40/60); (−20%; [−4% to −36%]). No proportional difference in recruitment was found between opt-in and opt-out groups varied by age, sex or socioeconomic status. The opt-in group had significantly more people in active decision-making roles (+30%; [10% to 50%]; p = 0.003). Non-significant trends were observed towards opt-in being less likely to include people with lower education (−11.8%; [−30% to 6.4%]; p = 0.13) and people who were not screened (−19.1%; [−40.1% to 1.9%]; p = 0.08). Opt-in was more likely to recruit people with a family history of colorectal cancer (+12.7%; [−2.8%, 28.2%]; p = 0.12).


The number of participants required to be approached was markedly increased in opt-in recruitment. Existing participants (eg, screening attendees) with a vested interest such as increased risk, and those preferring an active role in health decision making and with less education were likely to be recruited in opt-in. Research costs and generalisability are affected by implementing privacy legislation.

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