To identify outliers, upper and lower fences can be used to set limits of data scores. To find the fences, the quartiles of the data set must be found, leading to the IQR of the set. The formula for the upper fence is Q 3 + 1.5 IQR and the formula for the lower fence is Q 1 – 1.5 IQR.Click to see full answer. In this way, how do you find the upper fence of a box plot?Upper and lower fences cordon off outliers from the bulk of data in a set. Fences are usually found with the following formulas: Upper fence = Q3 + (1.5 * IQR) Lower fence = Q1 – (1.5 * IQR).Beside above, what is the upper fence in statistics? The Lower fence is the “lower limit” and the Upper fence is the “upper limit” of data, and any data lying outside this defined bounds can be considered an outlier. where Q1 and Q3 are the lower and upper quartile and IQR is the interquartile range. Regarding this, how do you determine outliers in a box plot? In order to be an outlier, the data value must be: larger than Q3 by at least 1.5 times the interquartile range (IQR), or. smaller than Q1 by at least 1.5 times the IQR. How are quartiles calculated? Quartiles are the values that divide a list of numbers into quarters: Put the list of numbers in order. Then cut the list into four equal parts. In this case all the quartiles are between numbers: Quartile 1 (Q1) = (4+4)/2 = 4. Quartile 2 (Q2) = (10+11)/2 = 10.5. Quartile 3 (Q3) = (14+16)/2 = 15.