PSY201H1 Chapter Notes - Chapter 6: Percentile, Interquartile Range, Percentile Rank
With normal distribution, we can determine percentiles and percentile ranks to answer questions about relative standing within a normal distribution. Percentile rank of a particular score is defined as the percentage of individuals in the distribution with scores at or below that particular score. We will always be concerned with the percentage on the left side of the x value. If the x value is above the mean, the proportion to the left will be found in column b = body of the distribution. If the x value is below the mean, everything to its left is reflecting in column c = the tail. Intermediate step of determining the z-score for that proportion of the distribution. Convert the z-score to an x value using the z-score formula. When population data form a normal distribution, there is a simple method to compute the interquartile range from the unit normal table.