NEA has refused to publish the 1h PSI despite demands from some quarters to do so. That really made some people quite upset. These people think that “the absence of a study doesn’t mean the absence of risk”. And they seem to suggest that there is therefore still a risk, just that no one bothered to find out.
That is fundamentally wrong. When NEA said that there are no studies to show that support 1h PM2.5 concentration that are harmful, it does not mean that no studies were done. It means that there were studies done to establish some link, but none of the studies found any correlation between 1h PM2.5 concentration and impact on health.
For people who are asking for 1h PSI to be released, I would like to ask this. Do you know what the PSI really is? Do you know how it is calculated? What is the basis of the way it is calculated? What does it take into consideration? What are PM2.5 particles? What other particles does the PSI take into consideration? What health impacts do each type of particles have on us? If we do not even know what the PSI actually is, then do we know what sort of correlation does the 1h PSI have with the quality of air? And how does that “quality of air” actually impact us?
It’s like… if I tell you that something is 100000 degrees celsius. Is that thing really hot? Yes. Is it dangerous? Depends. Because if that thing is just a tiny speck of dust and will only at most be in contact with your skin for 0.000001s, then is it still dangerous? Absolutely not. So was it meaningful for me to tell you that that thing was 100000 degrees celsius?
Another example. IQ. Is IQ of 150 smarter than IQ of 145? Depends. If one person is 50 and another is 25 now, and both took different IQ tests, and one took his test today, another took his test 10 years ago, then the IQ of 150 may be smarter, as smart or not as smart as the one who has IQ145. Because IQ is calculated from a normed distribution of people around the same age who did the same tests right around the same time.
Another example. Is someone who has a PSLE score of 250 smarter than someone who has PSLE score of 247? No. PSLE is also calculated from a normed distribution. So statistically, PSLE score of 247 is not significantly different from that of PSLE 250. But we would only know that if we actually know how PSLE T-score is calculated and have some understanding of statistics.
In other words, the context of any measure, of any “number” of any “index” is important. So unless we want to read all the science reports, and understand fully what that number really means, I think we do need to trust the professionals who have dedicated a good part of their lives understanding that number and what it really means. I fully support NEA’s decision. And I think we really need our citizenry to be better educated (not just trained) in science and scientific thinking.
[Featured image: by Chris McGrath/Getty Images]