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Drs Meier and Engstrom1 raise a number of issues regarding our paper and its conclusions.2 Their first concern is our use of the terms “precision” and “accuracy”, which they claim are incorrect. Although it is true that the term “precision” can be used to capture repeatability of a measurement (as Meier and Engstrom have reported themselves), it can be (and has been) also used in the fashion that we describe.3 Meier and Engstrom's assertion that our definition is incorrect is, therefore, incorrect—it is just different. The same goes for our definition of accuracy. It is correct that our results differ from previous studies, including those of Meier and Engstrom. We agree that this may be because of different measurement conditions. While test weighing may perform reasonably well under strictly controlled conditions (as Meier and Engstrom have shown), probably such conditions cannot be implemented in practice. It is not the performance of the test weighing under laboratory conditions that is important, it is its performance “in the field” (ie on a busy newborn ward under daily practical conditions) that counts. As our results clearly show, test weighing is an unreliable procedure to estimate milk intake under those conditions. This has been recognised by authors of other eletters.
The scale we used was carefully described, with the brand name, type number, design aim (to weigh infants in single grams) and measurement characteristics (we reported the repeatability—or precision, if we follow Meier and Engstrom's definition—of measurements which was very good, with a standard deviation of repeated measurements of <1 g or <0.5%). This should reassure Drs Meier and Engstrom that this scale was, indeed, designed to measure reliably down to the single gram. The measurement characteristics of our scale are not inferior to the scales used by Meier and Engstrom, which, in their words, were “specifically designed to detect such small differences in weight”. The Royal Dutch Pharmaceutical Society, whose published guidelines we followed, apparently uses stricter standards for weighing purposes than Drs Meier and Engstrom do. It would be shortsighted to call the American standard “incorrect”—it is just different. Although Drs Meier and Engstrom correctly raise the point that test weighing may be reliable under strictly controlled conditions, our results clearly show that it is not in daily clinical practice. That does not justify the qualification that our results are “incorrect” or theirs are correct. They are just different, and complementary. We believe that our results justify the abandoning of test weighing in daily clinical practice, and it seems from the other letters that this view is endorsed by others.