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AP Psychology Review Your Topics of Choice 2011-2012 UNIT TWO: RESEARCH METHODS Measures of Central Tendency “a measure of central tendency is a single score that represents a whole set of scores” • mean arithmetic average • median middle score/midpoint • mode most frequently occurring score An example: Data Set: 1,1,1,2,2,6,7,9,10 What is the mean? 4.3 the median? 2 the mode? 1 Range and Standard Deviation Averages that come from scores with low variability are more reliable than those from scores with high variability. So how do we know? range- gap between lowest and highest standard deviation- measures how much scores deviate from one another/from the mean When there is a lot of variability, the standard deviation will be large; when variability is smaller, the standard deviation will be smaller. Variability 35 30 25 20 Series 1 15 Series 2 10 5 0 10 20 30 40 50 60 70 80 90 100 Calculating the Variance 1. determine the mean 2. determine the difference between each score and the mean (the deviation) 3. square each deviation 4. calculate the mean of the squared deviations To get the standard deviation, simply take the square root of the variance. Which of the following is true of the two sets of scores in the chart? a. Set A has a larger standard deviation. b. Set B has a larger standard deviation. c. The range is the same for both distributions. d. Set A has a lower median score than set B. e. The mean score is the same for both distributions. Set A Set B 60 56 58 62 61 59 60 41 76 35 65 50 25. For a language test with normally distributed scores, the mean was 70 and the standard deviation was 10. Approximately what percentage of test takers scored 60 and above? a. 16 b. 34 c. 68 d. 84 e. 95 63. Which of the following sets of scores has the greatest standard deviation? a. 5,7,9,12 b. 2,7,9,22 c. 25,27,29,32 d. 50,51,52,53 e. 100,101,101,102,103 rational-emotive therapy • An approach to therapy that focuses on altering clients’ patterns of irrational thinking to reduce maladaptive emotions and behavior • “you feel the way you think” (Albert Ellis)