Abstract
We introduce the Newtonian Gravity Concept Inventory (NGCI), a 26-item multiple-choice instrument to assess
introductory general education college astronomy (“Astro 101”) student understanding of Newtonian gravity.
This paper describes the development of the NGCI through four phases: Planning, Construction, Quantitative
Analysis, and Validation. We discuss the evolution of the instrument through three versions, including the
refinement of a set of four concept domains and nine examples of items to illustrate how expert review, student
interviews, and Classical Test Theory statistics informed our approach. We conclude that the NGCI is a reliable
and valid instrument.