Investigators often face challenges when recruiting participants into randomized controlled trials (RCTs). Inadequate recruitment may prevent studies from detecting significant intervention effects
, cause delays, increase costs, and result in failure to complete trials
[2–4]. An understanding of effective strategies to improve recruitment into clinical trials is particularly relevant for trials of screening interventions, in which participants do not have overt, symptomatic disease so may not be as eager to participate in clinical studies.
A recent Cochrane review concluded that telephone reminders to non-responders, the use of opt-out rather than opt-in procedures (patients have to contact their physician to withhold contact details), and open designs (participants are informed about the treatment they are receiving in the trial) were all effective strategies in improving recruitment of participants to randomized clinical trials. However, some of these strategies have disadvantages. Opt-out procedures are controversial and open designs are unblinded
Some data suggest that telephone follow-up may lead to greater participant enrollment. The Prostate, Lung, Colorectal and Ovarian (PLCO) cancer screening trial demonstrated that the two centers with the highest yield incorporated telephone-based strategies in their recruitment methods: Salt Lake City investigators recruited other household members during follow-up telephone interviews, while Minnesota investigator increased their enrollment rates by 15% through follow-up telephone calls to non-responders four weeks after their initial mail invitations
Furthermore, two RCTs have examined the effectiveness of telephone reminders on recruitment. One study compared telephone reminders to no reminders on recruiting potential participants who did not respond to an initial mail invitation
. Another study compared telephone reminders to mail reminders on recruiting patients to an observational study
. The two RCTs found that telephone reminders can increase recruitment by nearly two-fold
[5, 7, 8]. Although promising, telephone-based follow-up is likely to be more time consuming and more costly than alternatives such as mail-based follow-up. Given that only one RCT has directly compared the effectiveness of telephone to mail reminders on recruitment, and that these investigators examined recruitment into an observational study and not into an interventional trial
, the extent to which telephone-based follow-up can increase enrollment compared to mail-based follow-up, particularly into an RCT for screening asymptomatic individuals, remains unclear.
In this paper, we compare the effectiveness of telephone versus mail-based follow-up using recruitment data from the SCOPE trial (Screening for Colorectal Cancer: a randomized trial of virtual colonoscopy, optical colonoscopy and fecal occult blood testing). The SCOPE trial is a study assessing the feasibility of conducting an RCT comparing three colorectal cancer screening interventions among participants enrolled from primary care practices in Ontario, Canada. To recruit patients into the SCOPE trial, potentially eligible patients (that is aged 50 to 70 years old) received a personalized, mailed invitation signed by their primary care physician to take part in colorectal cancer screening. This was based on successful recruitment strategies used in earlier cancer screening studies in our jurisdiction
[9–11]. For individuals who did not respond to this mailed invitation, we were uncertain whether telephone or mail follow-up would result in greater enrollment rates.
Therefore, the objective of the current study was to directly compare, among individuals who did not respond to an initial mailed invitation to take part in the SCOPE trial, the effects of telephone versus mail follow-up at four weeks on attendance rates with the study nurse for eligibility screening and enrollment rates into the SCOPE trial. We hypothesized that patients randomized to telephone-based follow-up would be more likely to attend for eligibility screening and be enrolled into the SCOPE trial than those randomized to mail-based follow-up.