The DXY is an indicator that many market watchers and commentators reference and quote. So what is the DXY or US Dollar index?
The DXY is a geometrically weighted index of some of the major trading partners of the United States. The composition if the DXY Index is heavily weighted towards the Euro and European countries that have not joined the European common market. The components of the DXY Index are (by weighting): Euro (57.6%), Japanese Yen (13.6%), Great Britain- Pounds Sterling (11.9%), Canadian Dollar (9.1%), Swedish Krona (4.2%), and swiss Franc (3.6%). Because of the composition of the DXY, it is sometimes referred to as the Anti-Euro Index.
The DXY is a convenient index to use as a simple method for referencing strength and weakness of the US Dollar (USD). But its ubiquity disguises the fact that it does not reflect the value of the dollar against a broad enough basket of currencies. The DXY was created by JP Morgan in 1973, and it has only been updated once, for the introduction of the Euro currency.
The DXY is heavily weighted towards European currencies, it underweight's the Canadian Dollar, as a proportion of US trade, and it largely ignores important Asian and Pacific trading partners, including Korea, Australia, Taiwan and necessarily China. Even if one were interested in including the Chinese Renminbi (Yuan) it would be both difficult and of questionable informational value to include the Renminbi because China keeps their currency pegged to a range that is based on the dollar.
A more accurate basket of currencies to track the relative value of the USD would be to value the dollar against the top US trading partners. The top 6 US trading partners, from high to low are: Canada, China, Mexico, Japan, Germany and the UK. It's hard to say why JP Morgan created this index and how it came into such prominence. One odd thing about this index is you can not trade it. There is no market that you can go to and buy the DXY. The closest you can get are futures and options contracts traded on the InterContinental Exchange (ICE).
If it's so inaccurate, then why is it so widely quoted? While there are more accurate ways to benchmark the USD, absolute precision is not always important for an indicator. Many traders and institutions likely have their own indices that they use to track the USD, but for the sake of comparison, it is very convenient to have a common index. The DXY is also highly correlated to a trade-weighted index most of the time. Relative strength or weakness moves by the USD represents huge flows of money. As I've written previously, the recent + 10% move by the DXY represents more than $ 1 trillion of nominal wealth destruction. Moves of this magnitude do not happen in a vacuum and the relative weakness of the DXY is mirrored by corresponding weakness in the trade-weighted index.
While there are shortcomings, the DXY does serve as a reliable indicator of USD strength and weakness and can be used as such, as long as one keeps in mind that it will occasionally be skewed if there are large currency moves that occur in the Euro.