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.
Early evening thunderstorms are common in summer, and tornados strike the state on a regular basis as Missouri is in America's Tornado Alley. January is the coldest month, with average high temperatures in the low 20's. July is the warmest month, with average high temperatures near 90 degrees. Much hotter summers and colder winters (with significant snow) are not uncommon. Annual precipitation amounts range from 35 to 40 inches in the northern half of the state. In the southern areas, amounts nears 50 inches are the norm.