Regression Standard Errors and Confidence Intervals
Our regression discussion has largely ignored the fact that our data come from samples. As we noted in the appendix to the first chapter, sample regression estimates, like sample means, are subject to sampling variance. Although we imagine the underlying relationship quantified by a regression to be fixed and nonrandom, we expect estimates of this relationship to change when computed in a new sample drawn from the same population. Suppose we’re after the relationship between the earnings of college graduates and the types of colleges they’ve attended. We’re unlikely to have data on the entire population of graduates. In practice, therefore, we work with samples drawn from the population of interest...
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