Are Index Investors Unknowingly Increasing Interest Rate Risk?

Here in an interestingly look at the Barclay's US Aggregate Bond Index from Lord Abbett  The below Chart shows how the duration of the Index has changed over the last ten years.

As you can see, up until late 2010 the duration of the Aggregate Bond Index tended to hover around 4.5 years. That has increased to approximately 5.5 years today. I think it is important that "passive" index investors be aware that they are currently making an "active" decision to increase their interest rate risk.