Michael “State of Fear” Crichton once proposed that UFOs were responsible for global warming. Why not? After all, something caused that record amount of snow in Detroit yesterday.
Don’t get me wrong. It was global warming which caused the snow—what else?—but something had to cause the global warming first. And that, as statistics demonstrate to a very high level of “significance”, was caused by UFOs. Roy Spencer has done the work “correlating” UFO reports and the environment. The statistics say it happened. (Thanks to KA Rodgers for reminding us of this.)
The statistics do prove the association. But nobody not actually preferring tinfoil-lined hats believes UFOs could be a cause of anything. Simultaneous movement in two (or more) time series, such as the increase in UFO reports and (say) ocean temperature, is a necessary condition to prove causality. But it is not a sufficient condition. Correlation does imply causation, but it is nowhere near proving it.
After all, since these two series moved together, it could also be that warming ocean temperatures are releasing more UFOs into the wild (the saucers have been parked down there, some say, for a very long time; hadn’t you seen John Carpenter’s The Thing?).
I apologize for the winding introduction, but it was absolutely necessary to begin with an absurd example of how plotting two or more time series together could lead to insanity. Because here comes another entry, also in the same genre. Not temperatures and ocean levels. But yet another thing the government is most anxious to control. Salt.
The new peer-reviewed article “Salt reduction in England from 2003 to 2011: its relationship to blood pressure, stroke and ischaemic heart disease mortality” by Feng He and others claims that the “reduction in salt intake is likely to be an important contributor to the falls in [blood pressure] from 2003 to 2011 in England. As a result, it would have contributed substantially to the decreases in stroke and [ischemic heart disease] mortality.” (Thanks to reader Rich for alerting us to this study.)
Feng He, like Crichton, plotted the course of several time series, but only over four separate years. The picture above shows some of these series. The data themselves were taken from different sources and measured over different people (and even over slightly different times, but let that pass). The sample sizes of the different data sets were widely different, too.
Emphasis: salt intake was measured on different people in each of the four time periods.
Of the most important series, “Stroke and IHD mortality rates were calculated as the number of stroke or IHD deaths divided by the population.” Of course, the population of England changed over this time, mostly due to immigration of people whose eating habits probably weren’t the same as the native residents’ (I’m guessing, but it’s plausible).
More emphasis: nowhere was salt intake nor heart disease nor stroke occurrence measured on any individual. All we have is four time points for several different disparate heterogeneous series. Nowhere was immigration measured. Obviously, or perhaps not obviously, many other possible causes were not measured.
There thus could be no possibility of claiming causation, nor even really hinting of it. Too many other things might have caused the decrease in deaths by IHD and stroke. And also, over those same four time periods, people in England still died. Each person that died had to die of something. Therefore if there were decreases in the rates of some diseases, such as IHD and stroke, there had to be an increase in the rates of some other disease or diseases. (I’m guessing cancer.) It is very curious we do not also see plotted these other causes. In just the same way, we can say salt was the cause of these increases.
Enter classical statistics: out pops wee p-values which are everywhere taken as proof that whatever the authors claim is therefore true. Sure, people know p-values aren’t proof; or at least that’s what they’ll tell you. But they believe it is, whatever they say.
Since salt was measured on different people than the outcomes, there is no proof that falling salt intake by a few hundred to thousand people means anything. After all, the first people sampled in 2003 may have been eating the same amount of salt through 2011. There is no way to know they hadn’t. This paper is thus not much different than Spencer’s plotting UFOs reports and ocean temperatures, except maybe Spencer’s is better since he used the same ocean throughout.
Anyway, here’s the kicker, the authors’ final word: “Therefore, continuing and much greater efforts are needed to achieve further reductions in salt intake to prevent the maximum number of stroke and IHD deaths.”
That speaks for itself. All uncertainty vanishes. The p-values are the final proof.
They’ll be coming after your salt next.