QMS 102 Lecture Notes - Lecture 6: Box Plot, Quartile, Interquartile Range
16 Nov 2017
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Document Summary
Quartile measures: quartiles split the ranked data into 4 segments with an equal number of values per segment. Find a quartile by determining the value in the appropriate position in the ranked data, where: 1st quartile position = (n + 1)/4 ranked value. 2nd quartile position = (n + 1)/2 ranked value. 3rd quartile position = 3(n + 1)/4 ranked value n is the number of observed values. If the result is a whole number then it is the ranked position to use. If the result is a fractional half (2. 5, 7. 5, 8. 5) then average the 2 corresponding data values. If the result is not a whole number or a fractional half then round the result to the nearest integer to find the ranked position. Iqr is q3-q1 & measures the spread in the middle 50% of the data. Iqr is also called the mid spread because it covers the middle 50% of the data.
