Beware The Bid-Ask Spread in ETFs

When the average Joe (or Jane) looks at transactions costs from trading, they typically focus on the commission charged by the broker. But in the case of some thinly-traded ETFs (exchange-traded funds), the bid-ask spread can add significantly to that cost. Here's a good piece on the topic from Morningstar:
No one has a very precise definition of liquidity, but it roughly boils down to how easy it is to buy or sell a particular security and how much agreement there is in the marketplace upon the security's fair value. The most liquid funds or stocks have miniscule bid-ask spreads, where the prices differ by only a penny. On the other side, a brand new ETF tracking a selection of more thinly traded mortgage-backed securities has a bid-ask spread near 0.80% as I write this. That means that buying and selling the fund at market prices, even without any commissions charges or price changes, would result in a 0.80% loss. Not exactly a terrifying loss, especially compared with what we all saw in 2008, but still an unwelcome drag on portfolio returns if it can be avoided.

Read the whole thing here