The team recorded body mass index measurements for study participants. Body mass index is calculated by dividing weight by height. For every one person with the disorder, researchers compared three people without it who were matched for gender, age and socioeconomic status.
The socioeconomic status of each person with the disorder was determined by where they live, using a national scoring system that considers factors like income, employment, health, education and access to services.
People in the study were then divided into five groups ranging from those with the fewest socioeconomic advantages to those with the most.
Overall, researchers found a six-fold increase in the number of cases of the disorder over the course of the study. In 2003, for every 100,000 people, 12 were living with the disorder, compared to 76 people in 2017. Also, in 2013, for every 100,000 people, two were diagnosed during that year, compared to eight people in 2017.