Biology 2244A/B Chapter Notes - Chapter 18: Sampling Distribution, Confidence Interval, Standard Deviation
25 Dec 2016
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Two sample problems: comparing 2 populations or treatments. 2 sample problem: can arise from randomized comparative experiments, randomly dividing subjects to 2 groups, exposing them to different treatments. Comparing random samples selected separately from 2 populations. No matching of individuals: can be different sizes. Goal of interference: compare average or typical responses in the 2 populations. Testing hypothesis of no difference: h0: 1 = 2 also 1- 2=0. We use sample mean and standard deviation to estimate unknown parameters. Whether observed difference in sample means is surprising depends on spread of individual observations and 2 means. Difference in sample means: is a statistic and has a sampling distribution. Center: the difference in the 2 variables means and the variance equal to the sum of the 2 variables" variances. We estimate sigma with standard error: estimated standard deviation. Usually, 1- 2 = 0, so the two-sample t statistic is.
