III.Section 2-3 A.Measures of Central Tendency 1.Mean – The sum of all data points divided by the number of values. a. This one is the one that we most often think of when we say “average”. 1) It’s also the one most affected by an extreme value (either high or low). a)Any value that has a z-score of less than -2 or greater than 2 is considered to be unusual b) Any value that has a z-score of less than -2.5 or greater than 2.5 can be called an outlier. 2.Median – the middle number (or mean of two middle numbers) when the data points are put into order. a.The point which has as many data values above it as there are below it. 3.Mode – The value that happens the most often (highest frequency). 4.Weighted Mean a.To find a weighted mean, multiply the mean of each category by its weight. Add the results of each category to get the weighted mean.

III.Section 2-3 B. Shapes of Distributions 1.Symmetric – Data bunched in the middle, with equal distribution on either side. 2.Uniform – Data is spread evenly across the whole spectrum. 3.Skewed Data – Named by the “tail”. a.Skewed right means most of the data values are to the left (low) end of the range. b.Skewed left means that most of the data values are to the right (high) end of the range.

4.Sample Measures of Variance a.Sample Variance – The sum of the squares of the deviations, divided by n - 1 (one less than the number of data points in the sample). b.Sample Standard Deviation – The square root of the sample variance. B. Empirical Rule 1.All symmetric bell-shaped distributions have the following characteristics: a.About 68% of data points will occur within one standard deviation of the mean. b.About 95% of data points will occur within two standard deviations of the mean. c.About 99.7% of data points will occur within three standard deviations of the mean.

V. Section 2-5 – Measures of Position A.Quartiles 1.Q 1, Q 2 and Q 3 divide the data into 4 equal parts. a.Q 2 is the same as the median, or the middle value. b.Q 1 is the median of the data below Q 2. c.Q 3 is the median of the data above Q 2. 2.Box and Whisker Plot a.Left whisker runs from lowest data value to Q 1. b.Box runs from Q 1 to Q 3, with a line through it at Q 2. 1)The distance from Q 1 to Q 3 is called the interquartile range. c.Right whisker runs from Q 3 to highest data value. d. To draw a box-and-whisker plot on the TI-84, follow these steps. 1)Enter the data values into L1 in STAT Edit 2)Turn on your Stat Plots (2 nd Y=), and select the plot with the box- and-whisker shown 3)Set your window to match the data a)Xmin should be less than your lowest data point. b) Xmax should be more than your highest data point. 4) Press graph. The box-and-whisker plot should appear. a)Press the Trace button and you can see exactly which values make up the Min, Q 1, Median, Q 3, and the Max.