Design of Experiments Illustrated by Weighing

A smiple weighing experiment is used to illustrate classical, factorial, fractional replicate of a factorial, confounded factorial and latin square designs of experiments.     

Directed acyclic graphs: An under-utilized tool for child maltreatment research

BackgroundChild maltreatment research involves modeling complex relationships between multiple interrelated variables. Directed acyclic graphs (DAGs) are one tool child maltreatment researchers can use to think through relationships among the variables operative in a causal research question and to make decisions about the optimal analytic strategy to minimize potential sources of bias.ObjectiveThe purpose of this paper is to highlight the utility of DAGs for child maltreatment research and to provide a practical resource to facilitate and support the use of DAGs in child maltreatment research.ResultsWe first provide an overview of DAG terminology and concepts relevant to child maltreatment research. We describe DAG construction and define specific types of variables within the context of DAGs including confounders, mediators, and colliders, detailing the manner in which each type of variable can be used to inform study design and analysis. We then describe four specific scenarios in which DAGs may yield valuable insights for child maltreatment research: (1) identifying covariates to include in multivariable models to adjust for confounding; (2) identifying unintended effects of adjusting for a mediator; (3) identifying unintended effects of adjusting for multiple types of maltreatment; and (4) identifying potential selection bias in data specific to children involved in the child welfare system.ConclusionsOverall, DAGs have the potential to help strengthen and advance the child maltreatment research and practice agenda by increasing transparency about assumptions, illuminating potential sources of bias, and enhancing the interpretability of results for translation to evidence-based practice.     

The effect of content and language integrated learning on students' English and history competences – Killing two birds with one stone?

By failing to appropriately control for selection effects, most previous research has overestimated the effects of Content and Language Integrated Learning (CLIL) on the development of students' foreign language skills. Furthermore, the CLIL-effect on the content subject is still widely unknown. Therefore, the present study investigated skill development of 1806 German CLIL and non-CLIL eighth-graders in English and History controlling for a wide range of student, classroom and teacher characteristics. Results of multilevel modelling confirmed that CLIL-classrooms showed greater increases in English listening comprehension but not general English skills as measured by a C-test than non-CLIL-classrooms. In History, the increases in subject knowledge over one school year were comparable despite CLIL-students' larger amount of instruction (three instead of two hours per week). The results confirm previous, differential findings for English. For the content subject, they indicate that CLIL-classrooms need to invest substantially more time to achieve comparable learning outcomes.