![]() You can calculate the interquartile range by hand or with the help of our interquartile range calculator below.Ĭalculate the interquartile range by hand Frequently asked questions about the interquartile range.Visualize the interquartile range in boxplots.When is the interquartile range useful?.Methods for finding the interquartile range.Calculate the interquartile range by hand.The First Quartile (Q1) is found by determining the median of the lower half of the data (not including the Median from the previous step when calculating the lower half data set median). ![]() This determination separates the data into two sets (an upper half and lower half).Determine the median (reference my post: Basic QA Statistics Series(Part 2)- Basic Measures of Central Tendency and Measurement Scales).Order the data set from smallest to largest.There are several methods for calculating quartiles, so the technique I am going to use is just what I consider the most basic without delving into any more in-depth math. Interquartile Range (IQR)- IQR is the Third Quartile minus the First Quartile and considered a measure of dispersion. Fourth Quartile (Q4)- This value is the maximum value in the data set (100% of the data are less than or equal to this value). It also does not have to be in the data set. Third Quartile (Q3)- This is the point at which 75% of the data are less than or equal to this value. The second quartile or median does not have to be a value in the data set. Second Quartile (Q2)- The value at which 50% of the data are less than or equal to this value. First Quartile (Q1)- The value at which 25% of the data are less than or equal to this value (does not have to be a value in the data set). First, to Define all of the aspects of IQR IQR is also a very useful tool to use to identify outliers (values abnormally far from the mean of a data set), but do not worry about the more in-depth math. IQR is best used with different measurements like median and total range to build a complete picture of a data set’s tendency to cluster around its mean. The IQR range, like the other measures of dispersion, is used to measure the spread of the data points in a data set. IQR is also a measure of dispersion, but as I’m sure you will be exposed to IQR in the future, I thought it best to give it a separate post. As promised, we are now covering the basics of Interquartile Range (IQR for short). When we left this small series on basic QA statistics, we had just discussed basic measures of Dispersion- Range, Variance, and Standard Deviation. However, applied science, particularly in the mass production of interchangeable parts, is even more exacting than pure science in certain matters of accuracy and precision. JuranįOR PROFESSIONALS/PRACTITIONERS: Both pure and applied science have gradually pushed further and further the requirements for accuracy and precision. JuranįOR ACADEMICS: Without a standard there is no logical basis for making a decision or taking action. It is only when we get down to the action words-measure, compute, prepare, check, endorse, recommend, approve-that we can make clear who is to do what. We can talk of who is responsible for budgets, or inventory, or quality, but little is settled. Gary Cox is a great Quality resource in addition to being very funny! FOR STUDENTS: A good rule in organizational analysis is that no meeting of the minds is really reached until we talk of specific actions or decisions.
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