Advance directives such as living wills and healthcare proxies are important tools for end-of-life decision-making, yet only about a third of American adults have them. Moreover, people who have chronic illnesses are only slightly more likely than others to have documented their wishes about end-of-life care.

This is according to a meta-analysis that was published in the July issue of the journal Health Affairs. Researchers analyzed 150 studies that were published between 2011 and 2016 and focused on the percentage of U.S. adults who had filled out an advance directive such as a living will, healthcare proxy or healthcare power of attorney.

Overall, the studies had covered about 800,000 people. The meta-analysis found that only 36.7 percent had completed any kind of advance directive. Of those, only 33.4 percent had completed healthcare proxies, and only 29.3 percent had filled out living wills. (About 32.2 percent of those who had completed an advance directive had done a combined version or some other type of document.)

What’s the difference between a living will and a healthcare proxy/power of attorney?

Different states have chosen to call some similar documents by different names, so the terminology can be confusing. However, the main difference among advance directives falls along the line between a living will and a healthcare proxy or power of attorney.

The intended audience for a living will, in general, is the doctor and hospital. A living will spells out what specific types of care you want provided or withheld in the event that you are dying and unable to communicate your wishes for yourself.

Some people fear that signing a living will indicates to doctors that the person doesn’t want any care provided at the end of life. In reality, it can tell physicians that you want certain care provided. It is not at all the same as a “do not resuscitate” order.

In contrast, the audience for a healthcare proxy or healthcare power of attorney is the person you designate to make end-of-life decisions for you. These documents both designate that person and can also provide guidance about what care you will want or not want at the end of your life. It’s essential to have a detailed conversation with the designated person, however; the documents give full authority to that person to act on your behalf if you are unable to communicate.

These documents can be changed at any time, although they generally require you to be in sound mind and they must be witnessed and sometimes notarized. Neither type of document can be used to override your wishes when you can communicate for yourself.

Medicare can reimburse physicians for counseling you and your beneficiaries about advance care planning.