on surveys, bed appears to affect about 1-2% at some point in their life, with 0.1-1% of people affected in a given year. bed is more common among females than males. there have been no published studies investigating the effects of bed on mortality, although it is comorbid with disorders that are known to increase mortality risks. economics since 2017, the number of cost-effectiveness studies regarding eating disorders appears to be increasing in the past six years. in 2011 united states dollars, annual healthcare costs were $1,869 greater among individuals with eating disorders compared to the general population. the added presence of mental health comorbidities was also associated with higher, but not statistically significant, costs difference of $1,993. in 2013 canadian dollars, the total hospital cost per admission for treatment of anorexia nervosa was $51,349 and the total societal cost was $54,932 based on an average length of stay of 37.9 days. for every unit increase in body mass index, there was also a 15.7% decrease in hospital cost. for ontario, canada patients who received specialized inpatient care for an eating disorder both out of country and in province, annual total healthcare costs were about $11 million before 2007 and $6.5 million in the years afterwards. for those treated out of country alone, costs were about $5 million before 2007 and $2 million in the years afterwards. evolutionary perspective evolutionary psychiatry as an emerging scientific discipline has been studying mental disorders from an evolutionary perspective. if eating disorders have evolutionary functions or if they are new modern "lifestyle" problems is still debated.