Luke Wainscoat and Sarah Turner have used data provided by Nick de Roos at the University of Sydney to depict the pattern of price changes for retail petrol in Perth, over the decade from 2003 to 2013. This video summarises that dynamic, in the form of a chart that shows:
- the change in the petrol price from one day to the next (cents per litre) on the vertical axis;
- the number of days since the beginning of the current petrol price cycle on the horizontal axis, where each cycle is taken to commence when the change in prices across all outlets is positive; and
- the degree of uniformity of price changes across outlets, with darker shades of red indicating that more petrol stations changed their prices by a given amount on a particular day of the cycle.
The video highlights that:
- petrol price cycles occurred frequently from 2003 to mid 2004;
- price cycles were few and irregular between mid-2004 and early 2006;
- fortnightly price cycles occurred regularly from mid 2006 to mid 2008; and
- a weekly price cycle began in early 2009, which became more prominent and regular from 2010.
The paper prepared by Nick de Roos and David Byrne with the same data is here.