The impact of sub-skills and item content on students’ skills with regard to the control-of-variables strategy

ABSTRACT

The so-called control-of-variables strategy (CVS) incorporates the important scientific reasoning skills of designing controlled experiments and interpreting experimental outcomes. As CVS is a prominent component of science standards appropriate assessment instruments are required to measure these scientific reasoning skills and to evaluate the impact of instruction on CVS development. A detailed review of existing CVS instruments suggests that they utilize different, and only a few of the four, critical CVS sub-skills in the item development. This study presents a new CVS assessment instrument (CVS Inventory, CVSI) and investigates the validity of student measures derived from this instrument utilizing Rasch analyses. The results indicate that the CVSI produces reliable and valid student measures with regard to CVS. Furthermore, the results show that the item difficulty depends on the CVS sub-skills utilized in item development, but not on the item content. Accordingly, previous instruments that are restricted to a few CVS sub-skills tend to over- or underestimate students’ CVS skills. In addition, these results indicate that students are able to use CVS as a domain general strategy in multiple content areas. Consequences for science instruction and assessment are discussed.

KEYWORDS:

• Control-of-variables strategy
• Rasch analysis
• scientific reasoning
• inquiry skills
• experimental skills
• assessment instrument

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Martin Schwichow owns a PhD in physics ecation. His main research interests are the development of scientific reasoning and inquiry skills.

Simon Christoph has a masters degree in physics and mathematics education and is currently working as a high school teacher.

Prof. William J. Boone is a specialist in the use of Rasch psychometric techniques to design and evaluate tests/surveys. He also specializes in the computation of Outcome Measures.

Prof. Hendrik Härtig works in the field of physics education. His main research interests are the role of language in science teaching and students' performance in scientific inquiry.

ORCID

Martin Schwichow http://orcid.org/0000-0001-9694-7183