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Statistics 2015: Announcements

Normal Table:  Table-Norm

In the final exam you will need a calculator.  You should have your own calculator and not borrow one in class, and you should know how to use it, so that you do not waste time during the quiz.

Percentiles (also known as quantiles):  we use the definition in Ross:

To find the sample 100p percentile of a data set of size n
1. Arrange the data in increasing order.
2. If np is not an integer, determine the smallest integer greater than np. The data value in that position is the sample 100p percentile.
3. If np is an integer, then the average of the values in positions np and np + 1 is the sample 100p percentile.

Example: if n=4 and the data is 2,5,6,9,  and p=0.25   (the 0.25 percentile is also called the first  quartile) then np is an integer.  According to item 3 above,  the first quartile is (2+5)/2.   Note that any number t  in [2,5] satisfies that at least 1/4 of the data are ≤ t and at least 3/4 are ≥ t.  We take the middle of the interval.  If n=5,  and the data is 2,5,6,9,11, then the quartile is  5.

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