Using Projective IRT to Evaluate the Effects of Multidimensionality on Unidimensional IRT Model Parameters.

The application of unidimensional IRT models requires item response data to be unidimensional. Often, however, item response data contain a dominant dimension, as well as one or more nuisance dimensions caused by content clusters. Applying a unidimensional IRT model to multidimensional data causes violations of local independence, which can vitiate IRT applications.

Understanding Alpha and Beta and Sources of Common Variance: Theoretical Underpinnings and a Practical Example.

Coefficient alpha estimates the degree to which scale scores reflect systematic variation due to one or more common dimensions. Coefficient beta, on the other hand, estimates the degree to which scale scores reflect a single dimension common among all the items; that is, the target construct a scale attempts to measure. As such, the magnitude of beta, relative to alpha, informs on the ability to meaningfully interpret derived scale scores as reflecting a single construct.

Evaluation of a walking school bus program: a cluster randomized controlled trial.

Background: The purpose of this study was to investigate the effects of a walking school bus intervention on children's active commuting to school.

Methods: We conducted a randomized controlled trial (RCT) in Houston, Texas (Year 1) and Seattle, Washington (Years 2-4) from 2012 to 2016. The study had a two-arm, cluster randomized design comparing the intervention (walking school bus and education materials) to the control (education materials) over one school year October/November - May/June).

Cohort Study of Downgraded Misdemeanor Convictions and Subsequent Violent Crime: Differences by Defendant Race and Ethnicity.

Introduction: Criminal convictions may be imperfect markers of criminalized behavior, in part because of criminal legal system processes (e.g., plea bargaining).

Low antibody levels associated with significantly increased rate of SARS-CoV-2 infection in a highly vaccinated population from the US National Basketball Association.

SARS-CoV-2 antibody levels may serve as a correlate for immunity and could inform optimal booster timing. The relationship between antibody levels and protection from infection was evaluated in vaccinated individuals from the US National Basketball Association who had antibody levels measured at a single time point from September 12, 2021, to December 31, 2021. Cox proportional hazards models were used to estimate the risk of infection within 90 days of serologic testing by antibody level (<250, 250-800, and >800 AU/mL ), adjusting for age, time since last vaccine dose, and history of SARS-CoV-2 infection.