Statistical quality control charts: New tools for studying the body mass index of populations from the young to the elderly
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- Ozilgen, S. J Nutr Health Aging (2011) 15: 333. doi:10.1007/s12603-010-0290-8
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Background and aims
Statistical quality control charts (SQCCs) have been widely used in numerous manufacturing processes to keep fluctuations within the acceptable limits but no applications have been applied to weight management studies yet. The aims of the present study were (1) to show that using the mean Body Mass Index (BMI) values as the only indicator to assess the weight status of populations might be misleading in clinical weight management studies; and (2) to introduce a powerful tool, SQCCs, to keep fluctuations in BMIs within acceptable limits in a given population for healthy aging.
The study design was cross-sectional. The distributions of individual BMIs (n=829) between specified limits (USL=24.9 and LSL=18.5) and the pattern of BMI change by age were studied using X-charts, tolerance charts and a capability analysis.
The mean BMI increased in both genders by age. In some groups, although a significant number of people were outside the normal weight BMI limits the mean BMI values were within the normal limits (18.5<BMI < 24.9). In addition, although the number of overweight individuals was greater in some groups, their mean BMIs were lower compared to the groups with fewer overweight individuals. Capability tests clearly show that each group, even the groups with a mean BMI in the normal weight ranges and also the groups which are referred as being “under control” according to the X-charts, was not in energy balance (Cp<l and Cpk<l).
The results clearly indicate that using the mean BMIs as the only indicator might be misleading in weight management studies. This study introduces SQCCs as a potential tool for clinical nutrition studies to maintain the fluctuations of individual BMIs within acceptable limits for healthy aging populations