Advance directives, like awarding power of attorney on health care decisions or completing a living will, haven’t been completed by most patients, including those with chronic illnesses, potentially complicating decisions by hospitals and physicians on end-of-life treatment.

In a Health Affairs study led by Kuldeep Yadav, research coordinator in the Palliative and Advanced Illness Research Center at the University of Pennsylvania, data for more than 795,000 patients involved in 150 studies between 2011 and 2016 were examined to determine the proportion of the population that had completed advance directives.

The two directives researchers looked for were healthcare power of attorney, which designates a surrogate or proxy to make treatment decisions if the patient is too incapacitated to do so themselves, and a living will, a written legal document specifying the patient’s preferences regarding the use of “life-sustaining therapies and other medical treatments in the event of incapacity or terminal illness.”

Most patients hadn’t completed those directives, the study found. Of the more than 795,000 patients, 36.7 percent had some form of advance directive, including 29.3 percent with living wills. Surprisingly, completion was only nominally higher among patients with chronic conditions (38.2 percent) than among healthy adults (32.7 percent).

The study did find differences when it came to the patient’s age and type. Patients ages 65 and over were more likely to have an advance directive (45.6 percent) than younger adults (31.6 percent), as were patients in hospice care (59.6 percent) and long-term care facilities (50.1 percent). Separating patients by primary disease, however, found only one category—neurological disease—where most patients had completed directives for end-of-life care.

Yadav and his coauthors said providers may be to blame for this lack of adoption, citing a common sentiment that advance directives have “failed to live up to their promise” and thus may not be promoted by physicians to patients.

“Future efforts are needed to improve the content and format of advance directives to better represent the substantive issues discussed in advance care planning conversations, such as patients’ values and goals, in addition to specific care preferences,” Yadav and his coauthors wrote.

Another issue may be the legal hurdles required to make such directives binding. These can include requiring two witnesses who aren’t family members, spouses or affiliated with providers to be present when directives are signed.

The study mentioned the use of advance directives has seemed to increase in recent decades. The fact that a majority of patients, especially those with chronic conditions, haven’t completed these documents suggests efforts need to be more focused on the patients likely to put these plans into action.

“Because advance directives remain a key component of high-quality advance care planning, increasing their completion rates remains a national priority,” the study concluded. “Specifically, policies and interventions should focus on populations with low advance directive prevalence rates and at high risk for poor end-of-life care outcomes.”