This research examined the issue of nonresponse bias and how it was reported in nonexperimental quantitative research published in the "Delta Pi Epsilon Journal" between 1995 and 2004. Through content analysis, 85 articles consisting of 91 separate samples were examined. In 72.5% of the cases, possible nonresponse bias was not examined in the…

Confidence intervals are widely accepted as a preferred way to present study results. They encompass significance tests and provide an estimate of the magnitude of the effect. However, comparisons of correlations still rely heavily on significance testing. The persistence of this practice is caused primarily by the lack of simple yet accurate…

All differential item functioning (DIF) methods require at least a moderate sample size for effective DIF detection. Samples that are less than 200 pose a challenge for DIF analysis. Smoothing can improve upon the estimation of the population distribution by preserving major features of an observed frequency distribution while eliminating the…

This article examines theoretical and empirical issues related to the statistical power of impact estimates for experimental evaluations of education programs. The author considers designs where random assignment is conducted at the school, classroom, or student level, and employs a unified analytic framework using statistical methods from the…

This article highlights the problem of omitted variable bias in research on the causal effect of financial aid on college-going. I first describe the problem of self-selection and the resulting bias from omitted variables. I then assess and explore the strengths and weaknesses of random assignment, multivariate regression, proxy variables, fixed…

Background: A literature search found five empirical studies of psychological treatment for adults with ADHD, out of 1,419 articles on ADHD in adults. Practice guidelines to date all recommend multimodal intervention, given that a significant number of patients cannot tolerate, do not respond to, or fail to reach optimal outcomes with medication…

A large sample technique attributed to L. Marascuilo, based on the multiple comparison technique of H. Scheffe, was programmed with the Statistical Analysis System (SAS), focusing on comparisons among independent binomial samples. Use of the SAS program is discussed. (SLD)

Reporting methods used in large-scale assessments such as the National Assessment of Educational Progress (NAEP) rely on latent regression models. To fit the latent regression model using the maximum likelihood estimation technique, multivariate integrals must be evaluated. In the computer program MGROUP used by the Educational Testing Service for…

Randomized controlled trials in educational research tend to be small. Small trials can have large, chance, imbalances in important covariates. For studies with sample sizes greater than 50, chance imbalances can be corrected using analysis of covariance; for small trials, however, statistical power is maximized if the trial is balanced and…

The primary objective of this study was to investigate how incorporating prior information improves estimation of item parameters in two small samples. The factors that were investigated were sample size and the type of prior information. To investigate the accuracy with which item parameters in the Law School Admission Test (LSAT) are estimated,…

Continues a series on topics in research methodology, statistics, and data analysis techniques for the library and information sciences. Focuses on the basics of sampling for surveys or experimental work, including rationale, terminology, technique, alternative methods, and sample size. (Author/LRW)

A sequential design utilizing identical samples was used to classify mixed methods studies via a two-dimensional model, wherein sampling designs were grouped according to the time orientation of each study's components and the relationship of the qualitative and quantitative samples. A quantitative analysis of 121 studies representing nine fields…

In negotiating to obtain a sample of records from a computer file, it is important to be able to present a simple program that will produce a representative and valid sample. This article describes two procedures: (1) an interval selection method; and (2) a random numbers file. (JAZ)

Large sample univariate methods are presented. These methods compare effect sizes within a single study between independent groups of different subjects on a single dependent measurement and independent groups that are assessed on the same dependent variable while using a different test. (TJH)

A small data set is used to show that correlations and standard deviations measured within an explicitly selected group need not be smaller than those within an applicant population. Both validity and reliability estimates within a selected group can exceed those within an applicant population. (Author/LMO)