Normalised histogram of r-values drawn from 100,000 Monte Carlo composites representing the null hypothesis (H₀). Data are Pearson’s r-values from the Oulu neutron monitor. The histogram has 101 bins over an x-axis range of −1 to 1. For comparison, a normalised Gaussian distribution is plotted on the dashed line: BA15 wrongly assumed the data possessed this distribution. A 4th order polynomial fit to the H₀ population is plotted on the solid line: this fit can be used to calculate the density (or probability, p) of a given r-value.