Quetelet (body mass) index: not an unbiased quotient
Body mass obviously increases in proportion to standing height. It is convenient to dispose of an index standardized for weight, as that would provide a convenient index of obesity. The Quetelet index (in English: ‘body mass index’, BMI) is used worldwide to this end: body mass/height². In children and adolescents this index still correlates with standing height. This is illustrated in the above figures based on data of a few thousand boys and girls in various European countries. It is therefore not an ideal index to establish the association between obesity and lung function. It would be better to use percentiles of body weight for standing height.