The charts below show the average course of prices over a total four-year period. Additionally each of the cycle’s four years is displayed separately.
The four-year cycle is determined by the US presidential election. For example, 2004 was an election year and the cycle years are:
| 2004: Election Year | 2006: Midterm Year |
| 2005: Post-Election Year | 2007: Pre-Election Year |
