ENVS278 Chapter Notes - Chapter 19: Statistical Hypothesis Testing, Null Hypothesis, Confidence Interval
8 Oct 2016
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The standard deviation of the difference between two proportions. Comparisons between percentages is much more common than questions about isolated percentages. Need a way to judge how large the sample difference is, this means we will need to estimate the standard deviation. The answer comes from realizing that we need to start with the variances and the. Pythagorean of statistics: the variance of the sum or difference of two independent random variables is the sum of their variances. Var (x-y) = var(x) + var(y) so . Independent assumption: within each group the data should be based on results for independent individuals. Randomization condition: the data in each group should ideally be drawn independently and at random from the target population or generated by a randomized comparative experiment. In fact, this may be the most important of these assumptions. Independent groups assumption: the two groups we are comparing must be independent of each other.
