ANALYZING THE RELATIONSHIP BETWEEN MATERNAL WEIGHT-GAIN AND BIRTH-WEIGHT - EXPLORATION OF 4 STATISTICAL ISSUES

Four statistical issues concerning the analysis of birthweight and mat ernal weight gain during pregnancy are discussed: (1) Part-whole corre lation is described (e.g. the correlation between total maternal weigh t gain and her infant's birthweight). (2) The choice between a ratio o r two separate explanatory variables is explored (e.g. body mass index or using maternal weight and height separately). (3) Two statistical proper ties (bias and power) when a binary variable replaces a continu ous variable are discussed (e.g. consequences of using low birthweight instead of reported birthweight). (4) A model selection procedure is presented to provide a way to select a useful subset of variables from a large number of available explanatory variables to model an outcome variable (e.g. birthweight). These issues are illustrated with a set of 4017 births from Moffitt Hospital at the University of California, San Francisco. Furthermore, these four issues arise in a number of app lications of statistical methods to data collected to study the epidem iology of newborn infants.