Design and data collection

Study design

Variables

  • Garbage company
  • Net weight of garbage

Statistician’s description of the design

The data set is simply a set of consecutive observations over time on a number of garbage trucks owned by 40 companies.

Statistician’s description of the problem

The problem is to determine if there are any characteristics of the observations that suggest that there is anything wrong with the weighbridge or the weighing procedures.

Protocol at the weighbridge

Inclusion criteria Every commercial garbage truck must be weighed at the tip weighbridge prior to entry to the tip and following dumping of their load at the tip.
Data to be recorded before entry to the tip The weighbridge supervisor records the following information for each vehicle:
  • Date
  • Company name
  • Total weight on weighbridge (in tonnes, to nearest 20kg)
  • TARE (empty weight of truck, as listed on the side of the truck, in tonnes to nearest 20kg)
Data to be calculated

The weighbridge supervisor enters the weight before entry and the TARE into a computer program. The weighbridge supervisor’s computer calculates:

  • Net weight of garbage = Total weight before – TARE
The computer automatically updates the daily records data file.
Data analysis Daily records are forwarded by the supervisor to the council for later analysis.