When First Numbers Matter: Efek Anchoring Bias terhadap Penyelesaian Soal Cerita Bilangan Cacah pada Siswa SD

This study aims to analyze the effect of presenting initial numbers (anchors) on anchoring bias in solving whole number word problems up to 10,000 among elementary school students. The method used is a quasi-experiment with a pretest–posttest nonequivalent control group design. The participants were 60 fourth-grade students of SDN 1 Citalang, divided into an experimental group and a control group. Data were collected through written tests, observation, and documentation, then analyzed using the Mann–Whitney U test and effect size calculation. The results show a statistically significant difference between the two groups, with a significance value of 0.011 (< 0.05). The mean posttest score of the experimental group (96.03) was higher than that of the control group (88.71), with an effect size of 0.33, which falls into the medium category. The conclusion of this study is that the presence of initial numbers in word problems influences the cognitive processes of elementary school students and indicates a tendency toward anchoring bias in this age group. Therefore, the presentation of mathematics problems needs to be designed more carefully to support the development of critical and objective thinking among students. Keywords: Anchoring Bias; Cognitive Bias; Elementary School; Whole Numbers; Word Problems