Measures of Center:
(We use these calculations to help us make general statements about our data. It is important that we choose the one that is most "centrally" located to best describe our data.)
Mean (average) - sum all the data points and divide by the number of data points that there are.
Median (middle) - put all the data points in order from leas to greatest and find the one in the middle. If there are an even number of data points, find the average of the two in the middle.
Mode (most) - the number that occurs the most often.
When we organized our data using a dot plot we noticed a couple of things:
When the data is symmetrical, the mean and the median are close together.
As the data becomes more skewed, the mean and the median become further apart because the mean is effected by the outliers.
The mean is the balance point of all the data, but it isn't always the most centrally located.
BIG IDEAS:
When the data is symmetrical, use the mean to descirbe the data.
When the data is skewed, use the median to describe the data.