Nonparametric Regression Estimation of Treatment Effects. Blood-sugar measurements are a common tool in diabetes testing. In a glucose-tolerance test, the glucose level in blood is measured after a period of fasting (fasting-glucose measurement) and again 1 h after giving the subject a defined dose of glucose (postprandial glucose measurement). Pregnant women are prone to develop subclinical or manifest diabetes, and establishing the distribution of blood-glucose levels after a period of fasting and after a dose of glucose is therefore of interest.The above Figure shows that bivariate nonparametric regression to the mean for glucose measurements for 52 women, with repeated measurements over three pregnancies. Circles are observed sample means obtained from the three repetitions of the standardized values of (fasting glucose, postprandial glucose). Arrows point from observed to predicted values. It is clear that different women have different treatment effects represented by the directions of the arrows.Reference: Müller et al (2003) . Reproduced with permission.
Willke et al. BMC Medical Research Methodology 2012 12:185 doi:10.1186/1471-2288-12-185