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:
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Average Weather in Joliet for February : Sunlight 5 hours a day: Coldest February temperature-29Â°C : Coldest daily temperature-6Â°C : Average daily temperature: 2Â°C : Warmest daily temperature: 4Â°C : Warmest February temperature: 21Â°C : Morning Humidity : 80%: Evening Humidity : 67%: Rain in February: 29 mm: Wet days for February: 9 days : Average Weather in Joliet for March