Drawing conclusions from samples—statistical inference—has been the subject of this chapter. Statistical inference is a central part of the scientific method since it involves the analysis of sample data gathered in the course of a scientific investigation.

Any quantity calculated from a sample is called a *statistic*. Statistics are thus random variables with probability distributions, means, and variances of their own. From the central limit theorem, we know that the mean of a sample, has, approximately, a normal distribution with mean and variance , where is the sample size and where and are the true population values; this theorem is a primary tool in establishing tests of hypotheses on single means and on the difference between means from two populations.

The purpose of this chapter is to establish tests of hypotheses and confidence intervals for some common parameters ...

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