Sorting out the rubbish – Analysis

The figure shows boxplots for companies with more than 10 weights recorded between January & June, 1997.


Ian Gordon disagreed with Dr. Johns’ analysis. Ian proposed alternative methods of assessing the weighbridge data; he suggested that the assumption that net weights were uniform over one tonne ranges was questionable, and commented on the selectivity of the analyses presented.

A puzzle solved

Click to hear from Ian Gordon

Questions to consider

  • Produce a graphical display that will make the problem with the weights of company 2 apparent to Council members.
  • Consider Dr Johns’ analysis. Review and comment on his assumptions.
  • Do you expect the distribution of net weights within a 1 tonne range to be uniformly distributed? Explain why or why not.
  • Draw graphical displays to describe the distribution of net weights within 1 tonne ranges for different companies.
  • Consider Dr. Johns’ conclusion about unusual counts within 1 tonne net weight ranges. Propose and carry out an alternative analysis for the 7 to 8 tonne range for company 11, assuming the uniform model. Are Dr. Johns’ conclusions reasonable in this case?
  • Repeat the analysis above for another weight range for company 11.
  • Dr. Johns chose subsets of the data to analyse. Is there a problem with this? How would you overcome it?
  • Has the Dr. Johns provided sufficient evidence for his conclusions? Explain why or why not.
  • Is there anything wrong with the weighbridge? Write a brief report to Council.