| Period | Causal relationship |
| January 1995 to August 2005 | WLI would cause a change of the first difference of WLI (0.71) |
| August 2005 to December 2008 | Oil prices would cause a change of the first difference of WLI (0.21) |
| December 2008 to August 2015 | The first difference of WLI would cause a change of oil prices (0.67) |