# Grouped Data Median Press Ctrl-A ©2009 – Not to be sold/Free to use Stage 4 Year 9.

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Grouped Data Median Press Ctrl-A ©2009 – Not to be sold/Free to use Stage 4 Year 9

Grouped Data In grouped data: Data classes must not overlap. Intervals must be of equal size. They are used for a large range of scores. A class centre (cc) is calculated by averaging the end points.

3 Cumulative Frequency Histogram/Polygon Histogram 0 1 23 45 5 10 15 20 25 30 Polygon xfCumulative Frequency cf 02 17 29 36 45 52 2 9 18 24 29 31 cf x Ogive

4 Median 0 1 23 45 5 10 15 20 25 30 cf x % 100% 0% 50% Median=2.1 for continuous data Median=2 for discrete data

5 Class Grouped Data – The Median 0-4 5-9 10-14 15-19 20-24 25-29 30-34 35-40 Class Centre cc 2 7 12 17 22 27 32 37 Tallyfcf 2 3 1 4 3 4 2 1 2 2+3 5 5+1 6 6+4 10 10+313 13+417 17+2 19 19+1 20 There are 20 scores. Therefore the median is the 10 th and 11 th scores. 10 th = 17 11 th = 22 Median = 17+22 2 = 19.5 Σf=Σf= 20

6 Grouped Data – The Median cc 2 7 12 17 22 27 32 37 f cf 2 3 1 4 3 4 2 1 2 5 6 10 13 17 19 20 |2|2 |7|7 | 12 | 17 | 22 | 27 | 32 | 37cc 5-5- 10- 15- 20- cf Cumulative Frequency Histogram Cumulative Frequency Polygon ‘Ogive’ Median Median (rounds up) = 22

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