At the start of the study, consistent breakfast eaters had an average body mass index of 21.7, intermittent eaters 22.5, and those who never had breakfast 23.4. Over the next five years, B.M.I. increased in exactly the same pattern. The relationship persisted even after controlling for age, sex, race, socioeconomic status, smoking and concerns about diet and weight.
The authors acknowledge that the study depends on self-reports of weight and eating habits, which are not always reliable, and that even though they controlled for many variables, the study was observational, showing only an association between breakfast eating habits and body mass, not a causal relationship.
socioeconomic Hide phonetics
related to the differences between groups of people caused mainly by their financial situation:
College Board officials said the difficulties arise more from socioeconomic than from ethnic differences.
body mass index
n. (Abbr. BMI)
A measurement of the relative percentages of fat and muscle mass in the human body, in which weight in kilograms is divided by height in meters and the result used as an index of obesity.兒童及青少年肥胖定義(BMI)
理想體重（公斤） = （正常範圍 BMI ）×身高2（公尺 2 ）
association v causal 統計學上的"相關" vs "因果"