Developing a two-tiered instrument with confidence levels for assessing students' conceptions of Direct Current circuits
Sabah, Saed Ahmad
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The purpose of this study is to develop and validate a two-tier revised instrument (DIRECT-TTC) for measuring students understanding of Direct Current (DC) circuits and identifying their alternative conceptions. Another main purpose of this study is to investigate the relationship between students' understanding of DC circuits and their confidence in their answers. The revised instrument consists of 15 two-tier items with a confidence scale. Both the Rasch analysis and students' interviews were used in validating the instrument and obtaining evidences for the validity of inferences. Through a two-stage quantitative and qualitative validation process using both conventional statistics and Rasch modeling, the results indicate that the instrument is both valid and reliable. The results show a statistically significant association between students' answers to the first- tier questions and explanations, r = .65 (p< .01, N = 214). The second-tier questions provided substantial information about students' conceptions of DC circuits beyond that provided by the first-tier questions. This research shows that the more able students with regard to the construct of understanding DC circuits are more likely to be confident in their answers, r = + .39 (p< .01). Several Rasch calibrations and correlation analyses indicate that the more difficult items are associated with less confidence in the correct answers. On the other hand, the results show no statistically significant relationship between item difficulty and students' confidence specifically in their incorrect answers. The difficult items with high confidence on incorrect answers exhibit the stronger alternative conceptions of DC circuits. The alternative conceptions of voltage and resistance are among the very strong alternative conceptions of DC circuits. Implications for researchers and teachers as well as recommendations for future research are presented.