  Employing the data from orbital periods and masses of extra-solar planets in
166 multiple planetary systems, the period-ratio and mass-ratio of adjacent
planet pairs are studied. The correlation between the period-ratio and
mass-ratio is confirmed and found to have a correlation coefficient of 0.5303
with a 99% confidence interval (0.3807, 0.6528). A comparison with the
distribution of synthetic samples from a Monte Carlo simulation reveals the
imprint of planet-planet interactions on the formation of adjacent planet pairs
in multiple planetary systems.
