# 1_17 - Measures of Central Tendency ( = so called average)....

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Measures of Central Tendency • The mean – The most popular measure of central tendency. – Mathematically, Sum of Scores / The Number of observations – It is not good when data are not symmetrically distributed, i.e., not good when data are skewed. • The Median – The mid point of the distribution, i.e., 50% of the data are below and above the point. – Frequently used for skewed data, e.g., income. (e.g.) 1,2,3,4,5 median = 3 2,2,3,8,9 median = 3 ( = so called “average”). • The mode – The most frequent score/category in a data distribution. – It is good for a nominal scale. – Rarely used in educational/psychological data. – Mathematical statisticians are often interested in the mode in the distribution of a infinitely large data.

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Measures of Dispersion • The variance 2 2 () i X X X N σ= This shows the mean of squared deviation scores • The standard deviation ( SD ) 2 2 i XX X X N σ=σ= - Mathematically, it is simply the square root of the variance.
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## This note was uploaded on 11/27/2011 for the course EDF 5481 taught by Professor Chiangshih during the Spring '07 term at FSU.

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1_17 - Measures of Central Tendency ( = so called average)....

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