Say is the average increase in shoe size for upper-class people compared to middle-class people: then the Wald test can be used to test whether is 0 (in which case social class has no association with shoe size) or non-zero (shoe size varies between social classes).
There are many different species of vultures and each has a different type of habitat. Turkey vultures are the most prominent of the New World vultures and can be found in Southern Canada, the Continental United States, Mexico, Central America and South America. These vultures live in small caves, beneath bushes, in hollowed out logs, and sometimes in abandoned structures.
Extraordinary eyesight is common to all vultures. Some also have keen sense of smell, but others have little sense of smell at all. New World vultures, native to the Americas, and Old World vultures, native to Asia, Africa and Europe, aren't close relatives at all, but they look a lot alike.