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John Hall

Your point is generally well-taken, but wrong in this specific instance. Particularly wrong around the time that earnings are released...

Your being wrong comes from not understanding where the -8.2% decline comes from. They are calculating it based on the close from the previous day. You are calculating the return relative to the opening price. What happens is that most companies report earnings after the market closes or before it opens. So the stock might have gapped down like -5% because analysts didn't like something in the earnings release.

There are few things you can do to isolate just the earnings impact. For instance, you can subtract out the impact of the market using an estimate of the beta of the stock and how much the market declined from the previous close to the open. This would isolate the stock-specific decline in Southwest. Then you could statistically test if this was a statistically significant change. Of course, most market participants would obvious recognize that a -5% decline on earnings day is statistically significant and don't need that analysis done. It's obvious.

The question, rather, is given that Southwest was down significantly, what was in the earnings release that analysts didn't like? Earnings and revenue were good for Q3. However, it seems like management has warned that 2019 costs are going to be ugly. So it's not a stretch to make the casual connection...

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