You should be aware that several different algorithms are commonly used to determine the values of quartiles. The concept is the same but the details of each method may differ.
For instance, the method we use in this course depends on a specific definition of "upper half" and "lower half." If you have an odd number of data values, you do not include the median in either half. This has become the popular method for teaching statistics in schools. It is also the method used in NCTM literature. Some statistics books or teaching materials, however, may use a slightly different method. For example, if you have an odd number of data values, you might include the median in both "halves." These two methods will sometimes produce the same or similar values for quartiles, but sometimes these values will be quite different, depending on the patterns and variation in your data.
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