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.
Missouri may be fifth on the list of average number of big tornadoes per year (2.2), but the town of Joplin was struck by one of the deadliest tornadoes in U.S. history. On May 22, 2011, the Joplin Tornado â with winds that exceeded 200 mph â killed 158 people and injured more than 1,000.