Normal curve distribution is a symmetrical distribution, which has a bell shape and identical scores for the mean (i.e., the average score), median (i.e., the middle score splitting the bottom 50% from the top 50% in the distribution), and mode (i.e., most frequent value). A bell-shaped curve (see an example in Figure 1) characterizing the normal distribution can be represented by the equation below:


where Y = frequency of a given value of X; X = any score in the distribution; µ = mean of the distribution (the mean or the average score is the ratio of the sum of all scores to the number of scores in the distribution); σ = standard deviation of the distribution (standard deviation is one of the variability measures representing ...

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