Fig. 2

Distributions of correlation data for heart rhythms in the Saudi Arabia group. (A) Density plots of correlations for observed vs. surrogate vs. swapped week distributions. The observed distribution (red) off to the right is generated from 1000 random split-half choices among the participants. The swapped week distribution (blue) closer to the center is generated from the same 1000 choices but with the first and second week swapped in the second half of the split. The surrogate distribution (green) in the center is generated from 1000 permutations of the HRV data, each with 100 split-half choices. (B) Histogram of regional mean correlations for the surrogate distribution, taking the mean over split-half choices. The red vertical line indicates the level of the observed regional mean correlation of 0.52 i.e. the mean of the observed distribution in pane A. It falls far in the tail and is less probable by chance than more than 99% of permutations to the left of the vertical line. The blue vertical line indicates the level of the regional mean correlation of 0.27 after swapping weeks, and it falls in the tail but not significantly.