Variance Estimation for the Horvitz-Thompson Total Estimator in Unequal Probability Sampling Designs

Self-reported nonceliac wheat sensitivity in an outpatient digestive endoscopy center: high frequency but insufficient medical approach.

Objective: 'Self-reported wheat sensitivity' (SRWS) is a self-reported condition caused by wheat ingestion in the absence of celiac disease or wheat allergy. The aim of the study was to investigate the frequency and characteristics of SRWS in outpatients referred for digestive endoscopy. Methods: The study, performed at the University of Palermo, enrolled 496 outpatients. Results: Seven individuals (1.4%) had an already established diagnosis of celiac disease. The questionnaire was administered to the other 489 individuals: 98 subjects (20%) were SRWS, the remaining 391 served as controls (i.e. not-SRWS). SRWS patients were younger (P < 0.001), with a higher percentage of females (P = 0.…

ConvergenceClubs: A Package for Performing the Phillips and Sul's Club Convergence Clustering Procedure

This paper introduces package ConvergenceClubs, which implements functions to perform the Phillips and Sul (2007, 2009) club convergence clustering procedure in a simple and reproducible manner. The approach proposed by Phillips and Sul to analyse the convergence patterns of groups of economies is formulated as a nonlinear time varying factor model that allows for different time paths as well as individual heterogeneity. Unlike other approaches in which economies are grouped a priori, it also allows the endogenous determination of convergence clubs. The algorithm, usage, and implementation details are discussed.