These examples are from the BAMS article “Continental US Hurricane Landfall Frequency And Associated Damage: Observations and Future Risks” by PhiliP J. Klotzbach, Steven G. Bowen, Roger Pielke JR., and Michael Bell.
The caption reads:
Fig. 2. (a) CONUS landfalling hurricanes by year from 1900 to 2017, and CONUS landfalling major hurricanes by year from 1900 to 2017. The dotted lines represent linear trends over the period. The p values for the linear trends are 0.33 for landfalling hurricanes and 0.61 for landfalling major hurricanes, indicating that neither of these trends are significant
If you haven’t already, read the article “Using P-Values To Diagnose ‘Trends’ Is Invalid”. This is a must.
See those lines over-plotted on the graphs of actual observations? Mesmerizing, aren’t they. Those lines did not happen.
This is an odd thing to say, and to insist upon; nevertheless it is true. The lines did not happen.
Take a look at 2 (b), at 2010. What happened in that year? Nothing. What does the line say that happened? Something.
“Come on, Briggs. Everybody knows the lines didn’t happen! Don’t mislead people. They’re just there as a guide.”
That so? A guide to what?
“A guide to the trend.”
That so? What’s the “trend”?
“Well, it’s that line, drawn by a regression with a non-wee p-value. Which means a horizontal line, and not the line drawn, can’t be rejected.”
I’ll assume you know what you’re saying when you said that, but you lost me. Are you trying to say that there was, as the line suggests, a downward multi-year linear force causing the number of major hurricanes to be less?
“No, I mean that a constant force causing major hurricanes can’t be rejected.”
Never mind that double-talk. Let’s assume the p-value was wee and the line therefore “real”, whatever that means. In fact, what does it mean? That a downward physical cause, a decreasing cause, a force that changes in just the little bit year-by-year indicated by the line operates on the atmsophere?
Hold up. In 2010, even if the line was horizontal, nothing happened, right?
That means that if the line, horizontal or decreasing was real, there should have been something like less than 1 major hurricane, but that something stopped this less-than-one major hurircane. Another cause or causes are out there that negated the force measured by the line?
“Something is causing major storms, of course.”
Certainly. We’re only arguing whether these trend lines have discovered cause. We don’t need them to see the data, which is right there in front of us. Have the storms increased? Sometimes yes, sometimes no. What caused that blip around 2005? What caused the blank right after? It wasn’t the line.
“That line could be discovering a force, and one that is decreasing in a strictly linear way, weakening, as you say, year by year.”
Sure, it could. Why not? It could also be false. How can we tell?
“By the p-value.”
But every use of a p-value is fallacious or a mistake. As has been proved. Anyway, it must sound strange to claim a mere statistical test can discover such a subtle and peculiar cause.
No, what we can do is to use that line, or something like it, to make predictions of future numbers. If that line or that something makes skillful predictions, in a technical sense, then we have something. If not, then not.
In any case, that line is not proof that hurricanes are doing anything. The observations alone are all we need for that.
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