Given these assumptions, we know the following. 1  The expected value of the difference between all possible sample means is equal to the difference between population means. 2  Thus, E(x 1 - x 2) = Î¼ d = Î¼ 1 - Î¼ 2. 3  The standard deviation of the difference between sample means (Ï d) is approximately equal to:
Guide to Joplin weather in December. The average maximum daytime temperature in Joplin in December is a cool 8Â°C (46Â°F). The average night-time temperature is usually a very cold -3Â°C (27Â°F). There are usually 5 hours of bright sunshine each day, which represents 51% of the 10 hours of daylight.
Volunteers look for victims of a devastating tornado in Joplin, Mo., on Tuesday. Credit Eric Thayer/Reuters The Sunday tornado â whose classification was upgraded by the National Weather Service on Tuesday to the most severe level, with winds exceeding 200 miles per hour â was the deadliest in a season in which twisters have killed more than 480 people. The Joplin tornado damaged nearly a third of the city. But workers were particularly concerned about a busy strip of big-box stores and densely populated apartment complexes that included Hampshire Terrace, where Becky Carithers returned Tuesday morning to the wreckage of her apartment.