We study the statistical significance of observed temporal variations of the solar active-region hemispheric helicity rule, as measured by the latitudinal gradient of the best-fit linear force-free-field parameter, dα/d . Using data from four different vector magnetographs, we compute and compare average annual dα/d values for these instruments for 19 years from solar cycles 21, 22, and 23. We find that although every instrument shows the "wrong" sign for the hemispheric rule in some years, there is no agreement among the instruments on which years are abnormal. None of the four data sets shows annual values of dα/d departing from the hemispheric helicity rule by more than 3 σ. We conclude that because the hemispheric helicity rule is a weak tendency with significant scatter, an annual subset of active regions is likely to produce statistically unreliable results.
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