Retaining Subjects Is Harder Than Recruiting Them


Applied Clinical Trials

Applied Clinical TrialsApplied Clinical Trials-10-01-2004

We work so hard to recruit subjects for clinical trials, so why don't we try harder to retain them?

We work so hard to recruit subjects for clinical trials, so why don't we try harder to retain them?

Doug Engfer, cofounder and CEO of invivodata

There is a lot of discussion about subject recruitment, but much less about retention. Why is that? When retention rates of 80% are considered "good," but dropout rates of 40% are common, there is definitely room for improvement. With that sort of dropout rate, a trial has to be at least 20% over-enrolled to compensate for the expected attrition.

And there is clear financial incentive to focus on reducing dropout rates-the Medici Group reports that the cost of retaining a subject is one-third to one-fifth the cost of recruiting a new one.1

Subject retention seems to fall victim to our sense of immediacy and desire to measure results. While subject recruitment is fairly easy to measure and relatively immediate, subject retention is a protracted process that has traditionally been difficult to monitor because there were no real-time tools available.

Potential benefits

If retention can be improved, then subject recruitment goals can be lowered. Furthermore, if subject compliance is optimized, then the trial power will increase and again fewer subjects will be required.2 And if fewer subjects need to be recruited, the trial can be shortened, thus saving both time and money. In addition, the number of subjects exposed to an investigational agent is thereby reduced, a significant benefit in its own right.

Generally, retention techniques focus on what I would refer to as rational or material inducements-gifts. However, I'd like to focus on some "softer," more emotional motivators that can pay real dividends based on our experience over the past several years.


Researchers can improve subject retention by finding out what motivates them to participate in medical research. These motivations will govern their in-trial behavior. Harris Interactive ranks subjects' participation motives as follows:

  • To advance medicine/science

  • Help others with the condition

  • Earn some extra money

  • For access to new treatments and to get better care for their disease or condition.

Trial design

Once identified, volunteers' motives can be used to help retain subjects for the duration of the trial. Take subjects' lives into account when planning the trial design. Anticipate and accommodate their needs, building systems and protocols that work for them. Measure endpoints that are clinically important, but make sure that the subjects understand why you are evaluating those factors and that they make sense. Patient education is particularly important in placebo-controlled studies to ensure that the subjects understand that they may derive no benefit from the compound under investigation.

In every trial, make sure that the burden on the subject is reasonable. Check to see if the number of visits, complexity of the tasks or physical distance from the site is influencing the dropout rate. And even more importantly, strive to maintain credibility with the subjects. If subjects learn that they can fabricate patient-reported outcome data, their commitment to the trial will be undermined.


Training not only helps to ensure that subjects know what to do, but also why they are doing it. Communication and education help create a successful relationship between the researcher and subject, and will ensure that the trial achieves the best possible results.


Frequent informed feedback can help reinforce positive behaviors and eliminate negative ones, especially if a subject-management system such as an eDiary is involved. However, the system and approach employed must accommodate the subjects' lifestyles, thus showing respect for them and their participation.

In summary, remember to address the whole person-understand, appreciate, and support each subject's motivations to keep them engaged. If subjects are engaged both rationally and emotionally, then trial retention rates can be raised and maintained at higher levels, saving time and money in clinical research.


1. The Research Roundtable, 3 (10) (March 2002).

2. Mckenzie et al., "Proving the eDiary Dividend," Applied Clinical Trials, 13 (6) 54–68 (June 2004).

Doug Engfer is cofounder and CEO of invivodata.

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