Two variants of the QPP period plotted against the flare impulsive phase duration. Left: full set of 37 flares with QPPs found by Pugh et al. (2017b). The Pearson correlation is 0.53 with a p-value of 0.0002, and the Spearman correlation is 0.50 with a p-value of 0.0006. Right: plot includes only those 20 flares that occurred within ±60° of the solar disc centre, and hence is the same sample of flares used in Figs. 4–7. The Pearson correlation coefficient is 0.56 with a p-value of 0.006, and the Spearman correlation coefficient is 0.65 with a p-value of 0.001.