Cumulative Frequency - used to find the median and the inter quartile range (IQR)

Add a 3rd column and do a running total of the frequency column A group of 50 nurses were asked to estimate a minute. The results are shown in the table. Time (seconds) Frequency 20 < t ≤ 30 2 30 < t ≤ 40 40 < t ≤ 50 9 50 < t ≤ 60 13 60 < t ≤ 70 17 70 < t ≤ 80 3 80 < t ≤ 90 90 < t ≤ 100 Cumulative Frequency 2 4 13 26 43 46 48 50 Scale for x axis, on your graph, is the end points of the class intervals We now need to show this information in a graph Scale for y axis, should be suitable for your data - as there are 50 nurses. Final value should always be equal to the number of pieces of data in the question.

Estimating a minute

Find the median and interquartile range Find the middle, ½ way up (median) of the data, ¼ (lower quartile) way up and ¾ (upper quartile) What now?? Upper quartile Median Lower quartile 66 secs 50 secs 60 secs

Results Median = 60 seconds Inter quartile range = upper quartile - lower quartile = 66 – 50 = 16 seconds

Let’s try some questions page 55