RAND Corporation

About: RAND Corporation is a nonprofit organization based out in Santa Monica, California, United States. It is known for research contribution in the topics: Health care & Population. The organization has 9602 authors who have published 18570 publications receiving 744658 citations.

Limiting the Risk of Bayes and Empirical Bayes Estimators—Part II: The Empirical Bayes Case

Abstract: We discuss compromises between Stein's estimator and the MLE which limit the risk to individual components of the estimation problem while sacrificing only a small fraction of the savings in total squared error loss given by Stein's rule. The compromise estimators “limit translation” away from the MLE. The calculations are pursued in an empirical Bayesian manner by considering their performance against an entire family of prior distributions on the unknown parameters.

Further investigation of the performance of S - X2: An item fit index for use with dichotomous item response theory models

Abstract: This study presents new findings on the utility of S - X2 as an item fit index for dichotomous item response theory models Results are based on a simulation study in which item responses were generated and calibrated for 100 tests under each of 27 conditions The item fit indices S - X2 and Q1 - X2 were calculated for each item ROC curves were constructed based on the hit and false alarm rates of the two indices Examination of these curves indicated that in general, the performance of S - X2 improved with test length and sample size The performance of S - X2 was superior to that of Q1 - X2 under most but not all conditions Results from this study imply that S - X2 may be a useful tool in detecting the misfit of one item contained in an otherwise well-fitted test, lending additional support to the utility of the index for use with dichotomous item response theory models Index Terms: item response theory, S - X2, Q1 - X, model = data fit, item fit index

Understanding trends in functional limitations among older Americans.

Abstract: OBJECTIVES: This report documents trends in functional limitations among older Americans from 1984 to 1993 and investigates reasons for such trends. METHODS: We applied logistic regression to data for noninstitutionalized Americans aged 50 years and older from the Survey of Income and Program Participation. We focused on 4 functional limitation measures unlikely to be affected by changes in role expectations and living environments: reported difficulty seeing words in a newspaper, lifting and carrying 10 pounds, climbing a flight of stairs, and walking a quarter of a mile. RESULTS: We found large declines in the crude prevalence of functional limitations, especially for those 80 years and older. Generally, changes in population composition explained only a small portion of the downward trends. Once changes in population composition and mobility-related device use were considered for difficulty walking, significant improvements in functioning remained for the 65- to 79-year-old group. CONCLUSIONS: Changes ...