It would be better to have just the beginning of each year marked on the x axis, rather than what I assume is auto-generated ticks (which are spaced every 3 quarters).

The vertical gridlines are very dense, to the point of being a distraction. It bothers me that they fade out before reaching the x axis, so that it's very hard to actually correlate them to a year/quarter.

It would be nice to embed a description of this index in the graphic, since very few people will have heard of it before.