Why does Vanguard rate most of their own ETFs as risky or very risky?

I am relatively new to investing and found interest in ETFs due to the diversification as well as the ease in buying them.

Vanguard has very high rated investments if you look on sites like Morningstar, which completely makes sense. Established company with an extremely solid track record and management.

When I was looking at Vanguard's screener for the ETFs they offered, all of them seemed to be either a 4 or 5, on a scale of 1 being the least risky and 5 being the most risky. This would make sense to me if I was looking at the ETFs based solely on stocks.

But I was looking at many of them, and even their high-credit quality bond ETFs like their Extended Duration Treasury ($EDV) are given a 5 on the risk scale. Why is this?

I thought it might be the fact that ETFs are passively managed and have the ability to be day traded, unlike mutual funds, but it still doesn't completely click as to why stock-based ETFs and bond-based ETFs are rated as equally risky.

Thanks in advance!

Submitted February 02, 2016 at 04:28PM by p_giggles http://ift.tt/1SWvJ2b