A report out today from the Pew Internet and American Life Project finds that seven out of 10 American adults track some kind of health measure. Weight, diet, and exercise are the most commonly monitored details, while some trackers keep a close eye on their own or a loved one’s conditions by watching health indicators such as blood-sugar levels or headaches.

The phone-based survey asked 3,014 U.S. adults about their self-tracking habits. One surprising finding was that nearly 50 percent of trackers in the survey say they do it in their head. Study author Susannah Fox calls these trackers the “skinny jeans trackers”—people who pay attention to whether or not their pants fit (who doesn’t do that?).

From the report:

This makes some sense since all someone might need to track their weight is a scale — or even a pair of jeans that only fit if someone is at their target weight. This finding is, however, a challenge to technology developers who would like to convince people to upgrade their habits. In order to capture this segment of the market they must strive to create a tool that is as seamless as keeping track in your head.

Another interesting tidbit was that people with two or more chronic conditions were more likely to track health indicators than people with only one. More than 60 percent of U.S. adults with two or more conditions (such as high blood pressure, diabetes, or asthma) track their symptoms; among survey responders with one chronic condition, 40 percent are trackers. People with multiple chronic conditions tended to be more serious about the task than other groups—they are more likely to update their notes on a regular basis and 70 percent shared their records with a doctor.

Overall, 63 percent of trackers said their self-monitoring habits has changed their approach to health care, sometimes leading to new questions for their doctor or impacted their decision on how to treat an illness.

And yet, only 3 percent of trackers with two or more chronic conditions used a mobile device such as a smart phone to keep their records. The mobile device arena bucked the general trend in the survey that people with chronic conditions took on more tracking than others. According to the survey, apps or other tools on phones or mobile devices are “significantly more popular among trackers reporting no chronic conditions, 10 percent of whom say they use an app to track their health.”

Despite these low numbers, Fox thinks there is still a lot of potential for the future of tracking gadgetry. As reported by Gigaom:

“We don’t have the answers in terms of what will change their minds or entice them to change their habits,[ said Fox]. What we do know now is how many people are doing it and already what impact that is having. Maybe in the future, if people can be seduced to upgrade to fancier technology that will actually move the needle on their heath outcome.”