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# 2.2

### Central Tendency

Spread of the data Standard Deviation A normally distributed sample spreads from -3 to +3 standard deviations from the mean
We should not use this measure of central tendency alone for decisions because it includes outliers Mean
The best measure of central tendency when making decisions Median
We use this measure of central tendency if we want to know what happens the most Mode (most can also be defined as typical or common)
If the mean is 50 and the standard deviation is 5, what is the probability of being between 45 and 55? 68.2% (of the sample will be within 1 standard deviation of the mean) 50 - 5 = 45 and 50 + 5 + =55
What are the three probabilities of the bell curve? 68.2% 95.4% 99.7%
68.2% of a sample will be within _______ standard deviation of the mean. 1
95.4% of a sample will be within ______ standard deviations of the mean. 2
99.7% of a sample will be within _____ standard deviations of the mean. 3
The mean is 20 and the standard deviation is 2, what is the probability of being between 14 and 26 99.7% (of the sample will be within 3 standard deviations of the mean) 20 + 2 + 2 + 2 = 26 and 20 - 2 - 2 - 2 = 14
_______ can be used to differentiate between two samples with the same mean. Variation
Which measurement can tell us where a single data point is on the bell curve? z-score. (Tip: Remember z for me. Where are you in the curve of your peers)
You want to know how your height compares to all of your family tree. How do you calculate a z score? (Your height - the mean of the family tree height) divided by the standard deviation of the family tree height (me-mean)/standard deviaiton
You are 63" tall and the family tree averages 67" with a standard deviation of 2". What is your z-score? (63-67)/2 = -2 You are 2 standard deviations shorter than the family tree.
Which measure lets you measure your height compared to your maternal family tree and your height compared to your paternal family tree? z-scores let us measure two samples by putting them to the same scale.
Created by: mgallo3