I wasn't sure whether or not the highlighted part belonged in the background The United States embarked on an era of reconstruction, with the painful history of slavery. The thirteenth, fourteenth and fifteenth amendments to the constitution were added to outlaw slavery. This would guarantee black citizens equal treatment under the law. However there was major resistance especially in the south. By the 1870's reconstruction fizled out, and the Jim Crow era began. This case begins in 1892, when Homer Plessy bought a first class ticket and was told to move to a different coach. Plessy refused, he was them thrown off the train and sent to a jail cell In a 1890 state law it reads railways within Louisiana are required to have "equal but separate" coaches. Plessy was put on trial in state court for breaking the law by sitting in the wrong coach. At trial Plessy argued that the law was unconstitutional, the government disagreed and the judge sided with the government.

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a hypothesis is an expected answer to a question, usually based on some theory or prior research. hypothesis testing is a method of determining the viability of a hypothesis. let’s use the us presidential election as an example. there are many hypotheses (questions) about how people feel or whom they will vote for. the only way to know the 100% “truth” about the answers to these questions is to ask every single possible voter – something that is impossible, expensive, time consuming etc. instead, we take samples and use statistics to make “best guesses” about the answer to a particular hypothesis. we never know for sure if our conclusion is right at the time we accept/reject it, but these techniques, when used appropriately can get us close to the truth most of the time (which is a lot better than guessing, flipping coins or throwing darts to get answers).

the tricky part about hypothesis testing is that we have to think somewhat backwards about it – we have to test what is known as the “null hypothesis”. as an example, the hypothesis might be “obama is more popular than romney” while the null hypothesis is “there is no difference in popularity between obama and romney”. we focus on the null hypothesis because it tells us exactly what the expected value of our tests should be (obama popularity = romney popularity) and we can collect data and see if it comes out that way (see next section on “significance”). if it does, then we “accept the null hypothesis” and reject our original hypothesis. if the null hypothesis is disproven, we look at the data to see if our original hypothesis holds (obama> romney).