In zoology, the phenomenon of fish moving excessively from one confined area to another is known as excessive transitory migration (ETM). To investigate the ETM of guppy populations, 40 adult female guppies were placed into the left compartment of an experimental aquarium tank that was 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, was monitored every minute for 30 minutes (Zoological Science, Vol. 6, 1989). If an equilibrium is reached, the researchers would expect the median number of fish remaining in the left compartment to be 20. The data for the 30 observations (i.e., numbers of fish in the left compartment at the end of the minute interval) are shown below. Use the large-sample sign test to determine whether the median is less than 20. Test using α = .05.

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GUPPY 16 11 12 15 14 16 18 15 13 15 14 14 16 13 17 17 14 22 18 19 17 17 20 23 18 19 21 17 21 17