Scientists wаnt tо determine whether the rаpid ecоnоmic growth in Chinа between 1950 and 2000 caused a mass extinction of animal species during that time period. A mass extinction event is considered to occur when the rate of species extinction far exceeds the background extinction rate. The scientists collected data on the number of extinctions of selected vertebrate species in China between 1950 and 2000, as shown in Table 1. Extinction rates were ascertained by measuring the average percent of species lost (PSL). Table 1. The average percent of extinctions of 252 protected vertebrate species in 2,365 counties in China from 1950 to 2000. Mammals Birds Amphibians and Reptiles Background Rate Average PSL ±1 standard deviation 47.4±33.59 19.75±17.70 28.80±28.86 27.21±16.20 Which of the following is the null hypothesis most relevant for evaluating the data in Table 1?