Are There Any Outliers? Using the 1.5*IQR Rule

Say we have the following data: 1,2,5,5,7,8,10,11,11,12,15,20 Notice that you must have ordered data before you can find the Five – Number – Summaries. Find the median first. It’s the middle point. Then find the quartiles, Q 1 and Q 3. They are the middles of the lower and upper half, respectively. The last thing to do is determine whether there are outliers using the 1.5*IQR Rule

min Q 1 Q 3 max 1,2,5,5,7,8,10,11,12,12,18, IQR = 12 – 5 = IQR is considered an outlier and will be a point in a boxplot and the ‘whisker’ ends at the last non-outlier data point * 7 = * 7 = -5.5