Purpose: In 2012 an influential publication used spatial analysis in the UK twin project TEDS to visualize the genetic and environmental influences on various childhood phenotypes based on geographical location (Davis et al., 2012). Also, a growing body of literature indicates that socioeconomic status moderates the genetic influences on academic achievement, especially in the US (Tucker-Drob & Bates, 2016). With this paper, we used spatial analysis and visualization to map the genetic and environmental influences on reading comprehension based on household geographical location in a twin project based in the US, where great economic inequality is seen. Furthermore, we mapped neighborhood income as a potential environmental moderator. Methods: The sample includes 2141 pairs of twins drawn from the Florida Twin Project on Reading, a sample that reflects the diverse population living across Florida. Reading comprehension was measured by the Florida Comprehension Assessment Test, and household income was be measured by US Census track median income. Results & Discussion. An environmental hotspot was seen in the Miami area, in that environmental variation was greater on reading comprehension in this region. In line with this, there was greater variance in neighborhood income in Miami. This suggests that neighborhood income is a moderator of reading comprehension based on geographic location. A second result was that less environmental variance was seen on reading comprehension in a band across the middle of the state (the “I-4 Corridor”, including Orlando). This was not reflected in differences in income variance, suggesting other environmental influences were serving as moderators in this region.
Davis, O.S., Haworth, C.M.A., Lewis, C.M., & Plomin, R. (2012). Visual analysis of geocoded twin data puts nature and nurture on the map. Molecular Psychiatry, 17(9), 867-874.
Tucker-Drob, E.M., & Bates, T.C. (2016). Large cross-national differences in gene×socioeconomic status interaction on intelligence. Psychological Science, 27(2), 138-149.
