Control of errors is most crucial when weights are collected over a short period (e.g., 1 to 2 weeks). When considering efforts to improve the reliability of measurements, it is useful to keep in mind their purpose. Factors that can affect measurements of a woman's weight include the type of scale used (e.g., spring or beam balance scale), the accuracy of its calibration, the clothing worn by the woman, the time of day the measurement is made, and the contents of the bowel and bladder at that time. However, measurement alone does not ensure accuracy. Weights measured in the clinic are preferable to self-reported or recalled weights. (1988) for a thorough review of methods and techniques. Before making any of the measurements described below, one should consult a reliable source such as Lohman et al. Therefore, the subcommittee believes it is premature to recommend specific techniques for making these measurements. Similarly, there have been no studies on pregnant women to validate the functional meaning of frame size indicators (e.g., elbow breadth and wrist circumference or diameter-measurements suggested as a basis for improving weight-for-height classification schemes). For reasons discussed in Chapter 6, the measurement of skinfold thickness to assess composition of weight gain and nutritional status during pregnancy has not been thoroughly studied or validated. Other measures, such as skinfold thickness and indicators of frame size, are also occasionally recommended but are not included in this critique. Therefore, major emphasis should be placed on establishing and implementing data collection techniques that provide the most reliable and accurate data possible for the particular clinical setting.Ĭlinical data relevant to gestational weight gain include weight, height, and gestational age. When weight and weight gain are used to screen individual women for special treatment or to monitor the progress of a pregnancy, the consequences of misdiagnosis resulting from poor data quality may be substantial. Methodological Issues Related to Data Collection in the Clinic
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