Growth mixture models (GMMs) are a popular method to uncover heterogeneity in growth trajectories. Harnessing the power of GMMs in applications is difficult given the prevalence of nonconvergence when fitting GMMs to empirical data. GMMs are rooted in the random effect tradition and nonconvergence often leads researchers to modify their intended…

Evaluators of education interventions are increasingly designing studies to detect impacts much smaller than the 0.20 standard deviations that Cohen characterized as "small." While the need to detect smaller impacts is based on compelling arguments that such impacts are substantively meaningful, the drive to detect smaller impacts may…

Morphological awareness has been assessed longitudinally for monolinguals and bilinguals to trace the developmental trend. Researchers have found the important role it plays in literacy development including vocabulary growth and reading development. Conclusions about the important role morphological awareness play in literacy development are…

Evaluators of education interventions increasingly need to design studies to detect impacts much smaller than the 0.20 standard deviations that Cohen (1988) characterized as "small." For example, an evaluation of Response to Intervention from the Institute of Education Sciences (IES) detected impacts ranging from 0.13 to 0.17 standard…

Background: The Education Endowment Foundation (EEF) is an independent charity that was established in 2011 with the explicit aim of breaking the link between family income and educational achievement in England. Over the seven years since its inception, EEF has contributed to the existing evidence base by funding over one hundred randomised…

Evaluators of education interventions are increasingly designing studies to detect impacts much smaller than the 0.20 standard deviations that Cohen (1988) characterized as "small." While the need to detect smaller impacts is based on compelling arguments that such impacts are substantively meaningful, the drive to detect smaller impacts…

In a randomized controlled trial, a decision needs to be made about the total number of subjects for adequate statistical power. One way to increase the power of a trial is by including a predictive covariate in the model. In this article, the effects of various covariate adjustment strategies on increasing the power is studied for discrete-time…

This study discusses six common methodological limitations in screening for language delay (LD) as illustrated in 11 recent studies. The limitations are (1) whether the studies define a target population, (2) whether the recruitment procedure is unbiased, (3) attrition, (4) verification bias, (5) small sample size and (6) inconsistencies in choice…

Latent growth curve modeling was used to describe longitudinal trends in community and religious involvement and Marcia's (1966) four identity statuses (diffusion, foreclosure, moratorium, and achievement), as well as to assess relations between involvement and identity change. Cross-lagged regression models explored temporal ordering of relations…

Presents formulas for estimating sample sizes to provide specified levels of power for tests of significance from a longitudinal design allowing for subject attrition. These formulas are derived for a comparison of two groups in terms of single degree-of-freedom contrasts of population means across the study timepoints. (Author/SLD)

The retention of older respondents in a longitudinal study is of important concern to data quality and representativeness of the target population. Participant non-response has been considered a more serious problem among older persons than among younger ones, since dropouts in longitudinal studies of older adults have been reported to be less…

The effect of interview length on wave nonresponse in a longitudinal survey was studied, controlling for respondent-specific characteristics known to affect survey response. Data from the National Longitudinal Survey of Youth were used, for a sample of over 10,000 people who were 14 to 22 years old when first interviewed in 1979. These individuals…

Reviews attrition rates in bereavement research and demonstrates prevalence of low acceptance rates and lack of knowledge about bias due to self-selection. Reports results of empirical study which showed effect of depression on willingness to participate: widowers who were less depressed agreed to participate; widows who were more depressed were…

Purpose: The purpose of this study was to determine strength gains following expiratory muscle strength training (EMST) and to determine detraining effects when the training stimulus is removed. Method: Thirty-two healthy participants were enrolled in an EMST program. Sixteen participants trained for 4 weeks (Group 1) and 16 participants trained…

Methods of using simplified time series analysis (STSA) in evaluating clinical programs are discussed. STSA assists in addressing problems of attrition/augmentation of subjects in programs with changing populations. Combining individually calculated "C" statistics in a simple aggregate analysis of restraint usage by nursing home staff…