(The median, midrange and midquartile are not always the same value, although they may be. Access to the complete content on Oxford Reference requires a subscription or purchase. In descriptive statistics, half the interquartile range, sometimes used as an index of variability. It is calculated as the difference between the two extreme. 9780199534067 Published online: 2009 Current Online Version: 2014 eISBN: 9780191726828 Find at OUP.com Google Preview semi-interquartile range n. It is obtained by evaluating Q 3 − Q 2 2. The interquartile range (IQR) is defined as the smallest of all the measures of dispersion. This makes it a good measure of spread for skewed distributions. The semi-interquartile range is affected very little by extreme scores. It is half the distance needed to cover half the scores. Semi-interquartile range is one-half the difference between the first and third quartiles. In the above example, the lower quartile is 52 and the upper quartile is 58.ĭata that is more than 1.5 times the value of the interquartile range beyond the quartiles are called outliers. In the previous example, the quartiles were. It is the difference between the upper quartile and the lower quartile. The semi-interquartile range is half of the difference between the upper quartile and the lower quartile. In the previous example, the quartiles were (Q1 4) and (Q3 11). Because it’s based on values that come from the middle half of the distribution, it’s unlikely to be influenced by outliers. The semi-interquartile range is half of the difference between the upper quartile and the lower quartile. The interquartile range is the range of the middle half of a set of data. When should I use the interquartile range The interquartile range is the best measure of variability for skewed distributions or data sets with outliers. If a variable y is a linear (y a + bx) transformation of x then the variance of y is b² times the variance of x and the standard deviation of y is b times the variance of x. The upper and lower quartiles can be used to find another measure of variation call the interquartile range. When distributions are approximately normal, SD is a better measure of spread because it is less susceptible to sampling fluctuation than (semi-)interquartile range. The median of the upper half of a set of data is the upper quartile (UQ) or Q3. The median of the lower half of a set of data is the lower quartile (LQ) or Q1. The median of a set of data separates the set in half. In a set of data, the quartiles are the values that divide the data into four equal parts.
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