I don't think you can consider a % change as a trend change indicator. I typically look at MACD & MA's (short or long term, depending on what your trading time frame is), & sustained break over/under key support & resistance levels. The most sure fire way to determine if a trend has changed is the simplest & oldest method used, that is, simply ask yourself, "is this market making higher highs & higher lows? (& vice versa)"
The thing about trying to use a % change, ESPECIALLY in stocks, is that it can fool you. If a stock is in a d/t, it can spike 10, 20, 50, 200%, whatever the case is, and the fact remains that sentiment is still likely bearish, and the trend is down. The trend isn't just your friend, it's your wife...don't argue with it, you'll just lose anyway!
