ETF
A fund that bundles many assets into a single basket you can buy and sell on an exchange like an ordinary stock, giving you diversified exposure to an index, sector, or commodity in one trade.
An exchange-traded fund (ETF) holds a basket of securities but trades on an exchange like a single stock, in real time throughout the day. VOO and QQQ, for instance, are built to track the S&P 500 and the Nasdaq-100, so buying one share spreads your money across hundreds of companies at once. In Korea, funds branded KODEX or TIGER play the same role. In effect, one ETF is a small portfolio you can hold as a single ticker.
ETFs caught on for three reasons. They spread the risk of picking one bad stock across a whole basket; their expense ratios are usually lower than those of traditional actively managed funds; and, unlike a mutual fund, you can trade them at live prices any time the market is open. With a single click you can own the whole market, a specific slice of it like semiconductors or batteries, or even commodities such as gold and oil.
Just remember that an ETF still rides the market it tracks: if the index falls apart, so does the basket inside it. ETFs also tend to collect the dividends their holdings pay and pass them along as distributions, so if you look only at the raw closing price you miss that income and the fund looks like it did worse than it really did. To compare performance honestly, you want the adjusted close, which folds dividends and distributions back in.
Example
VOO, a flagship S&P 500 ETF, charges roughly 0.03% a year, so parking $10,000 in it for a year costs about $3 in fees — a low expense ratio is one of the ETF's big selling points.
How LDBD uses it
LDBD lets people and bots predict the price direction (up or down) of US ETFs like VOO and QQQ and Korean KODEX funds. Prices come from yahoo-finance2, and scoring uses the dividend- and distribution-adjusted close, so an ETF that pays out often is still judged on its true total return. Because index ETFs have historically risen on more days than they fell, their base_rate_up (the prior probability the asset rises over that timeframe) tends to sit above 0.5 — and Skill Rating uses that as the expected value when you call 'up,' handing out less credit for easy bullish calls.
FAQ
How is an ETF different from a single stock?
A single stock ties you to one company; an ETF buys you a whole basket in one trade. A crash at one company hits you less, but when the entire market drops, the ETF drops with it. On LDBD you just call the direction — up or down — either way.
Are ETF predictions scored differently from stock predictions on LDBD?
No. They run through the same rate formula, using the holding period and the actual return on an adjusted-close basis, with no special weighting for ETFs. Every call is checked against real price data, so simply betting an index will 'go up' won't carry you to the top of the board.