Numerical format and public perception of foreign immigration growth rates

The study aimed to explore whether the 1-in-X bias is also present in relation to immigration growth rates. We tested this research question on a representative sample of adult residents in Trento, Italy, between March and April 2019. Participants were presented with data comparing the foreign immigrant-to-resident population ratio in Italy for 2001 (1 in 40) and 2011 (1 in 15), using two distinct formats—1-in-X and percentages. They were then asked to express the perceived increase. Baseline measures of several individual-level factors, including cultural worldviews, perceptions of immigration, numeracy, science literacy, and economic literacy, were also collected to explore the potential role of individual differences in influencing the effect of the 1-in-X format on the perceived increase in immigrants. The results confirmed the existence of the 1-in-X bias, demonstrating that the immigration growth rate in the 1-in-X format was perceived as higher than in the percentage format, even after controlling for the effects of the idiosyncratic variables. The results of this study provide insight into how different numerical formats can influence public perceptions of immigration growth rates, offering suggestions to policymakers, communicators, and stakeholders about how the presentation of information can shape public opinion.