STAT 100 Lecture Notes - Lecture 5: Standard Score, Percentile, Standard Deviation
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Bell shape normal distribution: all normal distributions are bell shaped, 68% is 1 standard deviation, 95% is in 2 sd from mean, 99. 7% is in 3 sd from mean. Normal or approximately normal = same: same as bell shaped and approximate bell shaped. Percentile- a value for which a specified percentage of all the values fall at or below: ex, q1= 25th percentile, median= 50th percentile, q3= 75th percentile. Table 8. 1: standardized score, z, proportion below z, proportions have to equal 1. After is . 9: percentile, proportion x 100. Z score represents the number of s. d an observed value is from the mean. If it"s less than the mean, it should be negative. 3: z=1, 1 standard deviation from the mean. 3: z= -1/3 or -. 33, below the mean. Common mistakes: follow puzzle don"t do bigger minus smaller number, it can be negative, do the subtraction first!!, not division.
