Research into the early United States frequently highlights the recurring use of the number 13 as a symbol of unity among the original colonies:

: A famous 2015 study attempted to replicate 100 psychology experiments, finding that only about one-third produced significant results, often with effect sizes half as strong as the originals.

: Research from the University of Miami notes specific psychological data points, such as 13% of the US population being affected by phobias. Labor Acknowledgement - Solid Ground

: The design features 13 arrows, 13 olive leaves, and 13 letters in the motto E Pluribus Unum . Official explanations from the National Archives and Wikipedia note these represent the "solid compact" of the several states.

: Modern social studies curricula, such as those in Louisiana , use "13" as a primary framework for teaching the founding principles, including economic terms like free enterprise and private property. Psychology and Research Contexts