Why do some potential CR subjects decline studies?

NIMH has some answers

Clinical trial sites go to a great deal of trouble to identify potential research participants, screen them, and then provide the necessary informed consent before they are enrolled in studies. But at some point in the process a proportion of potential volunteers say they're not interested.

Why? And how do you salvage some of this potential recruitment pool?

The main reason listed for why people ultimately decline to participate has to do with protocol procedures, according to data collected by the National Institutes of Mental Health (NIMH) of the National Institutes of Health (NIH) in Bethesda, MD. NIMH has data from over a decade of screening interested volunteers who decided after being pre-screened that they were not interested in participating in a study.

The NIMH data include people who voluntarily called about studies after seeing or hearing advertisements.

"The screens we completed from 1999 until the present identified patterns in the public, and, of course, we made many referrals to studies," says Julie Brintnall-Karabelas, MSW, LCSW-C, clinical research advocate of the human subjects protection unit of the Office of Clinical Director at NIMH. Brintnall-Karabelas and co-researchers presented an abstract with their findings at the 2009 PRIM&R Advancing Ethical Research Conference in Nashville, TN.1

"However, a unique group stood out, and this is why we decided to study recruitment," she says. "This is a group of individuals who called us, expressed an interest in participating, and they were eligible; however they declined participation."

NIMH had 965 people who were eligible, but who declined participation. These potential participants had a wide-range of diagnoses, including autism, Alzheimer's disease, anxiety, depression, bipolar disorder, obsessive compulsive disorder, post-traumatic stress disorder, and schizoaffective disorder.

"This is new territory and rarely has been explored," Brintnall-Karabelas says. "There isn't much information out there about eligible participants who decline."

Here are the trends investigators found:

  • 36% declined to participate because of protocol issues;
  • 33% declined to participate due to inconvenience or lifestyle issues;
  • 26% declined for other, non-specified reasons;
  • 3% declined for financial reasons;
  • 2% declined because they would like to participate in research elsewhere.

Recommendations for action

Investigators reviewed these findings and came up with a number of recommendations that researchers might follow to help improve their clinical trial recruitment.

The study was limited in its ability to further breakdown the reasons for declining to participate, but there were some trends, Brintnall-Karabelas says.

For example, those who declined for financial reasons were people who said they'd only participate in a study in which participants were paid, and the study for which they were eligible lacked the compensation they desired, she says.

Also, the 21 people who said they would participate in research elsewhere were mostly people who had responded to advertising about a particular study of repetitive transcranial magnetic stimulation (RTMS) to treat depression. When they found out they were eligible for a different study, but not for an RTMS study, they declined to pursue an RTMS study elsewhere, she adds.

For some of the potential participants, the protocol issues and inconvenience issues overlapped.

Some NIMH studies require lengthy inpatient stays of two months to nine months, Brintnall-Karabelas says.

"One of the things mentioned was the length of the study was too long," she says.

Some individuals who listed protocol reasons for declining had said they did not want to participate in a randomized, placebo-controlled trial because they were worried about being given the placebo, she says.

Another protocol issue involved the required wash-out period, which is the time a person who has been on medications takes to stop using drugs and let them wash out of his body," she explains.

"Some people expressed concern that their symptoms would get worse due to the wash-out of their medication," Brintnall-Karabelas says. "Some expressed an unease about the length of time spent in the MRI or the PET scans, and these might be related to claustrophobia."

Others had concerns about radiation exposure from the PET scans or having an arterial line placed in them or the medication side effects, she adds.

For a number of people in the inconvenience category, the issue was an inability to take time off of work to lack of transportation to get to the center.

So some of the concerns could be addressed with education or by other means, and some of the interviewers conducting the screening calls were able to change people's minds, Brintnall-Karabelas says.

For instance, if someone expressed concern about the MRI, then the interviewer might suggest they take a look at the MRI and see if they'd be comfortable with it. Or if someone is concerned about radiation from the PET scan, then the interviewer might let them know that it raises their risk of cancer in their lifetime from 25% to 25.03%, Brintnall-Karabelas suggests.

The study had no clear data on the people who didn't have a clear reason for declining participation, but some of the anecdotal evidence suggested a variety of reasons, such as symptom remission, concern about confidentiality, and an interest solely in homeopathic or alternative remedies, she says.

"For the inpatient studies, some people were concerned about losing their housing or losing their jobs," she adds. "However, NIH and NIMH have a large interdisciplinary team that has a specialization of social workers who can help participants maintain housing and work."

Often the concerns people have can be addressed through further education, Brintnall-Karabelas says.

"Education can really influence whether some people participate or not," she adds.


  1. Brintnall-Karabelas J, Cadman ME, Sung S, et al. Improving recruitment in clinical trials: why eligible participants decline. Abstract presented at the 2009 PRIM&R Advancing Ethical Research Conference. Nov. 14-16, 2009. Nashville, TN.