To improve survival and reproductive success, many species of fish have an evolved migration history. In one migration study of guppy populations (Zoological Science, Vol. 6, 1989), adult female guppies were placed in the left compartment of an experimental aquarium tank divided in half by a glass plate. After the plate was removed, the numbers of fish passing through the slit from the left compartment to the right one, and vice versa, were monitored every minute for 30 minutes. If an equilibrium is reached (which is optimal for survival), the zoologists would expect about half the guppies to remain in the left compartment and half to remain in the right compartment. Consequently, if 80 guppies were placed in the aquarium, the median number of fish remaining in the left compartment should be 40. Data for a similar 30-minute experiment involving 80 guppies is shown in the table below and saved in the GUPPY file. (Each measurement represents the number of guppies in the left compartment at the end of a 1-minute interval.) Use the large-sample sign test to determine whether the median is less than 40. Test using a = .05.
Based on Terami, H., and Watanabe, M. "Excessive transitory migration of guppy populations III: Analysis of perception of swimming space and a mirror effect." Zoological Science, Vol. 6, 1989.

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