chpt 3

# chpt 3 - Chapter 3 Central Tendency Central tendency is the...

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PSY230 Ch 3 Notes 1 Chapter 3 Central Tendency • Central tendency is the concept of developing or defining a SINGLE value that is representative of the distribution • What is “typical” for a large population • Not exact • Accuracy dictated by the shape of the distribution Three Main Measures of Central Tendency • Mean • Median • Mode Mean • Arithmetic average—add all the scores and divide by the number of scores • Mean of a population is symbolized by greek letter mu μ • Mean of a sample symbolized by M or X (X-bar) Calculation of the mean • Add up all the scores • Divide by the total number of scores • In words: Summation X divided by n Σ X n

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PSY230 Ch 3 Notes 2 The Mean The mean is the sum of all the scores divided by the number of scores in the distribution. Remember you can calculate the mean of a sample or a population Population Mean Sample Mean N X = μ n X M = Mean • Most sensitive of the measures of central tendency • Is changed when any one score is changed Other ways to think about the mean • If the total amount were divided evenly among all the members of the group, the amount each person would get would be the mean • The mean is the BALANCE point of the distribution—an equal weight of scores is above and below the mean. Figure 3.2 (p. 59) The mean is the balance point of the distribution Exactly like a scale. Moving or changing any one number will have an effect on where the balance point is. Characteristics of the Mean • Adding or subtracting a constant to each score will result in that same constant being added to the mean • Multiplying or dividing each score by a constant will result in the mean being multiplied or divided by that constant Computing the Mean from a Frequency Distribution Table Quiz Score (X) f fX 10 11 0 9 21 8 8 43 2 7 00 6 16 Total n = Σ f = 8 Σ fX = 66 M = Σ X/ n = 66/8 = 8.25 This is an adaptation of Table 3.1
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## This note was uploaded on 01/05/2011 for the course PSYC 230 taught by Professor Delaney during the Spring '08 term at Arizona.

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chpt 3 - Chapter 3 Central Tendency Central tendency is the...

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