Three different bootstrap methods for estimating confidence intervals (CIs) for coefficient alpha were investigated. In addition, the bootstrap methods were compared with the most promising coefficient alpha CI estimation methods reported in the literature. The CI methods were assessed through a Monte Carlo simulation utilizing conditions…

In this article, the authors talk about variation and how variation between measurements may be reduced if sampling is not random. They also talk about replication and its variants. A replicate is a repeated measurement from the same experimental unit. An experimental unit is the smallest part of an experiment or a study that can be subject to a…

Research regarding the prevalence of psychiatric conditions co-occurring with intellectual disability in adults was reviewed. Particular attention was paid to the qualities of sampling and diagnostic methodology, which have been identified as needs in two recent reviews. Sixteen articles published in peer-reviewed journals between 2003 and 2009…

Often researchers face situations where comparative studies between two or more programs are necessary to make causal inferences for informed policy decision-making. Experimental designs employing randomization provide the strongest evidence for causal inferences. However, many pragmatic and ethical challenges may preclude the use of randomized…

This study examines the proposed Reliability Generalization (RG) method for studying reliability. RG employs the application of meta-analytic techniques similar to those used in validity generalization studies to examine reliability coefficients. This study explains why RG does not provide a proper research method for the study of reliability,…

Birnbaum raised important challenges to testing transitivity. We summarize why an approach based on counting response patterns does not solve these challenges. Foremost, we show why parsimonious tests of transitivity require at least 5 choice alternatives. While the approach of Regenwetter, Dana, and Davis-Stober achieves high power with modest…

The importance of sample size, although widely discussed in the literature on structural equation modeling (SEM), has not been widely recognized among applied SEM researchers. To narrow this gap, we focus on second language testing and learning studies and examine the following: (a) Is the sample size sufficient in terms of precision and power of…

Methodologies to identify and enumerate children outside of family care vary as do the vulnerability categories of the children themselves. Children outside of family care is a broad term encompassing children absent of permanent family care, e.g., institutionalized children, children on/of the street, child-headed households, separated or…

Background: Behavioural problems are common in people with intellectual disability (ID) and are often treated with antipsychotics. Aim: To establish the frequency and characteristics of people with ID included in randomised controlled trials (RCTs) on antipsychotic treatment for behavioural problems, and to investigate the quality of these RCTs.…

Mean length of utterance (MLU) is a frequently used measure of the expressive language of young children. The suggested conventional, contemporary, clinical practice is to calculate it from a language sample of a minimum of 50 to 100 contiguous intelligible utterances. This practice places considerable strain on professionals working with young…

This article proposes that sampling design effects have potentially huge unrecognized impacts on the results reported by large-scale district and state assessments in the United States. When design effects are unrecognized and unaccounted for they lead to underestimating the sampling error in item and test statistics. Underestimating the sampling…

Using exogenous characteristics to identify endogenous subgroups, the approach discussed in this method note creates symmetric subsets within treatment and control groups, allowing the analysis to take advantage of an experimental design. In order to maintain treatment--control symmetry, however, prior work has posited that it is necessary to use…

Ramsay-curve item response theory (RC-IRT) is a nonparametric procedure that estimates the latent trait using splines, and no distributional assumption about the latent trait is required. For item parameters of the two-parameter logistic (2-PL), three-parameter logistic (3-PL), and polytomous IRT models, RC-IRT can provide more accurate estimates…

How can humans acquire relational representations that enable analogical inference and other forms of high-level reasoning? Using comparative relations as a model domain, we explore the possibility that bottom-up learning mechanisms applied to objects coded as feature vectors can yield representations of relations sufficient to solve analogy…

A jack knife is a pocket knife that is put to many tasks, because it's ready to hand. Often there could be a better tool for the job, such as a screwdriver, a scraper, or a can-opener, but these are not usually pocket items. In statistical terms, the expression implies making do with what's available. Another simile, of an extreme situation, is…