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Standard Deviation

Standard Deviation. A measure of variability Commonly used to calculate other statistical measures Shows the distance (difference) between the mean and the steepest part of a normal curve Indicates dispersion , or spread, of scores in a distribution. Standard Deviation.

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Standard Deviation

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  1. Standard Deviation • A measure of variability • Commonly used to calculate other statistical measures • Shows the distance (difference) between the mean and the steepest part of a normal curve • Indicates dispersion, or spread, of scores in a distribution

  2. Standard Deviation • The smaller the standard deviation, the more tightly clustered the scores • The larger the standard deviation, the more spread out the scores

  3. Standard Deviation On an average day in Los Angeles, the number of sudden deaths from cardiac causes is about 4.6. On the day of the Northridge earthquake, there were 25 such deaths, 24 of which occurred after 4:31 a.m., when the earthquake struck.

  4. Standard Deviation Make your prediction: Will the average male or the average female who died from sudden cardiac causes on the day of the earthquake be older? A. the average female was older B. the average male was older

  5. Predict whether the ages of the males or the ages of the females who died on the day of the earthquake were more variable. A. ages of males were more variable B. ages of females were more variable

  6. Ages of females who died: 66 92 75 84 83 80 Ages of males who died: 90 38 59 45 47 67 79 75 66 71 68 62 51 55 62 56 56 64 The Data

  7. 66 92 75 480/6 = 80 84 83 80 480 90 38 59 45 47 67 79 75 66 71 68 62 51 55 62 56 56 64 1111 1111/18 = 61.7 Calculate the Mean

  8. X - X = s 66 – 80 = -14 92 – 80 = 12 75 – 80 = -5 84 – 80 = 4 83 – 80 = 3 80 – 80 = 0 ss2 -142 = 196 122 = 144 - 52 = 25 42 = 16 32 = 9 02 = 0 399 (sum of squares) Subtract the mean from each score

  9. s2/N (N-1) 399/5 = 79.8 sd = s2 79.8 = 8.93 There it is! The standard deviation for the ages of the females who died that day is 8.93. Now you try the same formula for the ages of the males. Find the variance; find the square root of the variance

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