Many people think of statistics as a scary subject involving lots of numbers and equations. While it is true that statistics can be quite technical, the subject remains highly relevant to modern life. For example, before booking a hotel, we might check the number of good and bad online reviews. When we make investment decisions, we might also review the relevant financial and statistical data first. In this chapter we shall discuss some general principles for interpreting statistical studies, without going too much into the mathematical details.

Many statistical studies investigate samples. We study a sample to infer general conclusions about a population, the set of things we are interested in. Suppose we want to find out whether heavy metal contamination in vegetables is a serious problem in China. The population is then all the vegetables in the whole of China. But it is obviously impossible to test all of them. So instead we collect a variety of vegetables from different places in China. This is our sample and we shall measure the amount of heavy metal contaminants in this batch. If the study is done well, it will give us a good picture of the overall situation in China. However, if the study is not done correctly it might not just be a waste of time and money. Policy decisions based on a bad study can have harmful consequences.


Here are some questions we should ask if we want to evaluate a statistical study. ...

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