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It is axiomatic that a mathematical model is only as strong as the number of assumptions on which it is based. Based on the methods reported in the development of these models, it is possible to identify several false assumptions which have been made, and incorporated into the models.

Addressing the study by Elad et al. [20] first, one of their key conclusions (from the technique shown in Fig. 2A–C) is that milk removal from the breast is caused by the rigid up/down movement of the baby’s jaws (impacting on the base of the nipple), combined with intraoral negative suction pressure. As a consequence, their model is based solely on the action of negative suction pressure, without any consideration of the possible role for the positive pressure wave created by the dorsum of the baby’s tongue. It should therefore come as no surprise that their model predicts that negative suction pressure alone can fully account for milk removal from the breast; essentially, theirs is more a kinetic model of how a mechanical breast pump works.

A key quality issue, likely to affect the validity of modelling studies, is the size of the sample on which any model is based. In the study by Elad et al. [20], 9 subjects, varying in age from 11 to 150 days were included, with a maximum of 15 s of sucking recorded. From these records, “four to six sucking cycles (i.e., about 150 frames) were selected for the analysis of tongue motion.” On the basis that six suck cycles last approximately 6 s, this signifies that data from a total of 54 s of feeding were used to generate the mathematical model. This may be a reason why Elad et al. [20] did not detect, or include in their analysis, the type of tongue movement described by Geddes and colleagues [11, 12–14].

Certain assumptions may also be made to make a model less mathematically complex to compute. Mortazavi et al. [21] state that, in their study, the milk ducts are “assumed to be rigid.” An unstated corollary to this will be that the duct openings are also assumed to be rigid, being held open (patent) throughout the feed. This is recognized as a false assumption, as, in practice, the milk ducts are highly flexible and collapsible; it would not be easy to predict how they would behave dynamically under the combination of both positive pressure from the tongue and negative suction pressure from the oral cavity. Their model also assumes that negative suction pressure plays the sole role in milk removal. Perhaps as a consequence of this, a comparison of simulated data with clinical data from the same baby forces them to conclude that “suction pressure alone cannot account for milk removal from the breast” (the probable factors were discussed above).