Using Projection Splines to Explore Differences in Distributions
Whitehead, N., Liu, J., Li, L., & Hsia, J. (2009, August). Using Projection Splines to Explore Differences in Distributions. Presented at Joint Statistical Meetings 2009, Washington, DC.
We adapted a method of comparing distributions that uses projection splines, which fit a regression line that allows the slope changes over the range of x, for use with complex survey data. We used SUDAAN to estimate the percentile distribution of gestational age among the infants of black women and those of white women. We calculated y as the difference between the percentile of the two groups divided by the variance of the difference and assumed y was identically and independently distributed. We compared the distributions by regressing y on the average of the two percentiles, starting with a model with a node every 7 days. We eliminated nonsignificant nodes stepwise until all nodes were significant at an alpha = 0.01. The final model had 6 significant nodes, indicating the gestational age distribution of infants of black women is shaped differently from that of infants of white women.