PSYCH 370 Lecture Notes - Lecture 6: Standard Deviation, Probability Distribution
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The z score of an observation xi, taken from a population with mean and standard deviation , is denoted by z and is calculated as follows: z = (xi - ) / . The z score is a measure of the number of standard deviations that an observation is above or below the mean. Since s is never negative, a positive z score indicates that the observation is above the mean, a negative z score that the observation is below the mean. Note that z is a dimensionless value, and is therefore a useful measure by which to compare data values from two different populations (and thus possibly measured by different units). The standard normal distribution (snd) or normal curve . Recall from the readings, lecture 12 normal distributions, that the standard normal distribution is the same as the normal curve.
