Cumulative Frequency

Programme Outline

Jamie is to witness the action at the UK Snakeboard Championships, whilst Katie finds out about the UK National Sizing Survey.

Jamie meets snakeboarder Rick to learn about the sorts of stunts that are going to gain favour with the championship judges. He completes a frequency table to monitor the scores gained by the competitors and adds another column to work out the cumulative frequency. By drawing a cumulative frequency graph, Jamie hopes to find out whether Rick's score will place him in the top half, or even the top quarter of the field. Katie looks in more detail at the graph Jamie has constructed. She explains the terms median and upper and lower quartile and shows how to locate and read them from the graph. Back to the competition to see how well Rick has done.

Katie visits the London College of Fashion having volunteered to be measured for the UK National Sizing Survey. A state-of-the art scanner takes up to 130 measurements within seconds, and can even produce 3D computer models of body shape.

Using the data on inside leg measurements for 16 to 30 year olds, Katie produces a cumulative frequency curve and calculates the median and quartiles. She summarises the data using a box plot (or box and whisker diagram). She identifies on the diagram the interquartile range and the overall range for the data. Katie then compares the box plot for 16 to 30 year olds with a box plot for 31 to 54 year olds. Sue Fairly, who has been involved in the survey, helps her to interpret the differences between the two sets of data.

In this week's Tick or Trash, Katie and Jamie draw a cumulative frequency graph and estimate the median. Katie explains how she made a mistake in reading the median from her graph.