Sample surveys typically gather information on a sample of units from a finite population and assign survey weights to the sampled units. Survey frequently have missing values for some variables for some units. Fractional regression imputation creates multiple values for each missing value by adding randomly selected empirical residuals to predicted values. Fractional imputation methods assign ...

Imputation using a regression model is a method to preserve the correlation among variables and to provide imputed point estimators. We discuss the implementation of regression imputation using fractional imputation. By a suitable choice of fractional weights, the fractional regression imputation can take the form of hot deck fractional imputation, thus no artificial values are constructed afte...

Regression predictors are usually entered into a model without transformation. However, it is not unusual for regression relationships to be distinctly nonlinear. Fractional polynomials account for nonlinearity through real-valued power transformations of primary predictors. Adaptive methods have been developed for searching through alternative fractional polynomials based on one or more primar...

BACKGROUND AND PURPOSE ADC provides a measure of water molecule diffusion in tissue. The aim of this study was to evaluate whether the fractional change in ADC during therapy can be used as a valid predictive indicator of treatment response in head and neck squamous cell carcinoma treated with chemoradiotherapy. MATERIALS AND METHODS Forty patients underwent DWI at pretreatment and 3 weeks af...

Consider a finite population of N elements identified by a set of indices U = {1, 2, ..., N}. Associated with each unit i in the population there is a study variable yi and a vector xi of auxiliary variables. Let A denote the set of indices for the elements in a sample selected by a set of probability rules called the sampling mechanism. Let the population quantity of interest be θN = ∑N i=1 yi...

Mass spectrometric analyses of peptides mainly rely on cleavage of proteins with proteases that have a defined specificity. The specificities of the proteases imply that there is not a random distribution of amino acids in the peptides. The physico-chemical effects of this distribution have been partly analyzed for tryptic peptides, but to a lesser degree for other proteases. Using all human pr...