Chi Square statistic is a nonparametric statistical procedure that is used to compares the totals between categorical data. It is one of the most used types of nonparametric statistic which can be a one-way or two-way. The number of data two be compared is not limited to two as it can be several categories independent of each other. It is commonly used to compare an observed data with an assumption. The larger the value got from solving the Chi-Square this just means that the values of the two are apart thus the null hypothesis has proof to say that it is true and there is a statistical importance between the observed and the assumption (null hypothesis).
Chi Square is commonly used when testing for pesticides in laboratories, in agriculture related areas, and health related issues and lab tests. Chi-Square tests can be used to conduct a goodness fit between the observed data and the expected data (assumption). For example, if we want to test if there is an association between the amount of fish yield between persons that didn’t attend a fishing school and fishermen who attended fishing school using the line and sinker method. The question that we can have is Is a Fisheries degree associated with the amount of catch using line and sinker fishing? Hypothesis could be that Fishermen who have gain educational degrees in Fisheries Education catch more fish using line and sinker, while the null hypothesis could be that there is no significant association between a Fisheries education degree and the amount of fishes caught using line and sinker. In short, this test would want to know if a fisheries education has an effect on the amount of fishes caught. This can be useful to Fishing companies who uses this kind of fishing because obviously, if there is proof to say that Fishermen with degrees can catch more then they will start hiring fishermen who have already gained their degrees but the trade-off is of course, they have to pay higher salaries compared to hiring undergrads.
Math.hws.edu (2013). The Chi-Square Statistic. Retrieved from http://math.hws.edu/javamath/ryan/ChiSquare.html
West (2013). Use of the Chi-Square Statistic. Retrieved from http://ocw.jhsph.edu/courses/fundepiii/PDFs/Lecture17.pdf