I like statistics - at least the ones that make sense. One oft-quoted phrase about these mathematical manipulations is:‘There are lies, damn lies - and statistics’. This has been attributed to Mark Twain, Benjamin Disraeli and Winston Churchill (amongst others), although it seems that Churchill only wished he had coined the remark.
Statistics are used by just about everyone from baseball enthusiasts and medical practitioners to newspaper reporters. One number that caught my eye recently was the claim that about five trillion cigarette butts are discarded each year. Before passing this remarkable number along to colleagues, (1 followed by 12 zeros) I thought I’d do a quick “back-of-the-envelope” calculation. This is a technique popularized by Enrico Fermi, one of the many brains behind the development of the atomic bomb. He would make a rough calculation on a scrap of paper to see if the numbers associated with some proposed process were in the right ballpark.
Let’s see - assuming there are seven billion people in the world, of whom, estimating conservatively, one billion smoke at a rate of 10 cigarettes a day for a year, we come up with a total of about 3.7 trillion cigarettes. Cough..cough. Thus, the reported number and my estimate are not that far from each another. They are of the same “order of magnitude,” meaning that they do not differ by a factor of ten.
If we assume that the original number of five trillion is correct, then the weight of those butts would be five trillion times the weight of one butt. So off I went looking for butts on the street. It did not take long to find a few and weigh them. The average was about 0.15 grams. This means that about 1.6 billion pounds of butts are discarded each year, translating to some 800,000 tons. That’s roughly the weight of half a million automobiles chopped into very small bits and spread all over the world. Another way to put this would be that the weight of all those cigarette butts is about equal to the weight of all of the vehicles registered in the Province of New Brunswick.
The above calculations were done by making reasonable estimates and doing one weighing of a few butts and taking an average. Admittedly, having a sensitive balance available is not so common, but even that estimate could have been made by just going to Google and asking the question. One cigarette weighs a bit less than one gram, so one-sixth of that (reasonable estimate) is about 0.15 grams. The point is that unusual statistics can often be checked by an individual, either by back of the envelope calculations or by inserting a few key words into Google. For example, in this case, just Googling the words “how many cigarette butts”-yielded the desired result. The second listing was a site based on U.S. Department of Agriculture data and verified the total cigarette number along with the weight of the filters. That site also revealed that the total world production of cigarettes has been essentially constant over the past 20 years.
The real message here is that an individual can often make a decent estimate of a statistic, but these days, a search engine will quickly corroborate of refute the number. It is important to not simply pass on data seen in the press without some simple checking of the facts. It should also be pointed out that the butt of a cigarette is made of cellulose acetate, a material that does not easily biodegrade. Estimates of how long these stick around to annoy us range from 1 to 15 years. But don’t trust me. Check it out.
Dr. David Harpp
McGill University