A test of significance for periods derived using phase-dispersion-minimization techniques

A test for determining the statistical significance of periods derived using phase-dispersion-minimization techniques (Lafler and Kinman 1965; Stellingwerf 1978) is described. The test is based on Fisher's Method of Randomization, is simple to perform, and can be easily incorporated in standard period-finding programs. It is most valuable in situations where measurement signal-to-noise ratios are low. The secondary periods of five recently discovered double-mode RR Lyrae stars are evaluated using the method.