False Cause: Ignoring Common Cause
Bertha Alvarez Manninen
There is increasing evidence that the easy availability of welfare has greatly increased the incidence of child poverty. For example, the highest increases in the rate of child poverty in recent years have occurred in those states that pay the highest welfare benefit.
White House Task Force Report, 2013
In general, the false cause fallacy occurs when the “link between premises and conclusion depends on some imagined causal connection that probably does not exist” (Hurley 2015, 149). There are three different ways an argument can commit the false cause fallacy: post hoc ergo propter hoc; cum hoc ergo propter hoc; and ignoring common cause. We’ll deal with ignoring common cause here. Also see the chapters for post hoc ergo propter hoc (Chapter 80) and cum hoc ergo propter hoc (Chapter 78).
The fallacy of ignoring common cause occurs when one notices a constant correlation between A and B and assumes A caused B (or vice versa) while ignoring that there is a third variable, C, that causes both and therefore accounts for the correlation. As Sheila Morton (2014) notes, the quotation above from the White House Task Force report commits this version of the false cause fallacy because “the report ignored many other, more probable, causes of the rising rates of childhood poverty: inflation, job loss, the massmovement of manufacturing to overseas plants that took place during the
Reagan era. All these are more likely causes of childhood poverty than the availability of welfare” (98). Indeed, these reasons can explain both the rise of childhood poverty and the rise of the availability of welfare without making the latter causally responsible for the former.
Harkening back to the smoking example given in Chapter 78, consider the following: “coffee drinking and lung cancer are associated, but coffee drinking doesn’t cause lung cancer, nor vice versa.
They are associated because both are associated with cigarette smoking. Smokers happen to drink more coffee on average than non-smokers” (McKay Illari et al., 2011, 16). In this case, the tendency to smoke is the common cause that accounts for the correlation between excessive coffee drinking and lung cancer. Ignoring this common cause in an observational study (as was done in the example in Chapter 78 concerning HRT and coronary disease) could lead to the conclusion that it is the coffee drinking itself that increases the risk of lung cancer (thus instilling an unfounded fear among coffee drinkers who are non-smokers).In general, it is widely agreed that “breast is best” - that is, that a woman’s breastmilk is a superior source of nutrition for human infants than formula. Countless studies illustrate a causal relationship between breastfeeding and various health benefits for the mother and the infant. One benefit that has been the subject of debate, however, relates to the finding that breastfeeding is positively correlated to higher IQs in children and whether this implies a causal relationship between breastmilk and childhood intelligence. One concern is that asserting this causal relationship ignores an important confounder (the correlation between two variables that can be explained by appealing to a common third variable) - that women who breastfeed “also often provide a more enriched and cognitively stimulating environment for the child” and that “breastfeeding is associated with higher socio-economic factors that may be the true cause of enhanced intellectual ability” (Jacobson and Jacobson 2002, 258). In other words, it may not be the breastmilk itself that contributes to a child’s higher IQ scores; rather, the tendency toward breastfeeding and providing a mentally stimulating environment for a child has a common cause: membership in a higher socio-economic group.
The belief that marijuana use has a causal relationship with the use of harder drugs may also suffer from this fallacy.
Again, while it may be true that users of drugs such as heroin or cocaine started experimenting with drugs using marijuana, it may be that the use of both has its roots in a common cause (poor judgment, a reaction to certain socio-economic or psychological factors, or simply basic curiosity about the effects of these substances), which is different from asserting that it is the marijuana itself that leads to the use of more dangerous drugs.Sometimes it isn’t clear exactly which version of the false cause fallacy applies. An advertisement for Eukanuba dog food implies that Utah, a 17- year-old dog, has lived for 30% longer than his expected lifespan because he has been fed this brand. There is no indication that any kind of substantial study has been done to illustrate that Eukanuba dog food causally contributes to a dog’s increased lifespan, and so, as it stands, the ad commits the false cause fallacy. If what the advertisers mean to say is that the causal connection exists because eating the food precedes the dog’s increased lifespan, then this is a post hoc ergo propter hoc fallacy. If what they mean to say is that the two (the dog’s diet and his increased lifespan) occur simultaneously and therefore a causal connection can be inferred from this alone, then the ad commits the cum hoc ergo propter hoc fallacy. In addition, the ad may be ignoring that there could be a common cause that explains both the dog’s diet and his longer lifespan - perhaps the dog has the kind of owners who are particularly mindful about their dog’s health and this contributes both to buying expensive food for him and also to ensuring his health in other ways. In any case, there is no reason to believe from this ad alone that this particular brand of dog food itself has a direct causal connection to Utah’s increased lifespan.
In 2009, the Kellogg Company settled against charges that its advertisements for Frosted Mini-Wheats were deceptive. The ad claimed that the cereal was “clinically shown to improve kids’ attentiveness by nearly 20%” (Federal Trade Commission 2009).
What it neglected to mention is that the study compared children who had eaten the cereal to children who hadn’t eaten any breakfast at all. The study, therefore, did not show that Frosted Mini-Wheats itself causes better attentiveness but rather simply eating something for breakfast increases attentiveness. The commercial exploited the false cause fallacy (in particular the post hoc ergo propter hoc) to get consumers to buy its product. This fallacy is also present in many of the arguments concerning the alleged connection between vaccines and autism despite the plethora of evidence otherwise. These examples, among many others, highlight the importance of familiarity with fallacious reasoning - the consequences of not being able to distinguish good reasoning from bad reasoning extend outside the classroom and into the depths of society.For further reading, Tyler Vigen’s (2015) website Spurious Correlations is a humorous illustration showing that correlative events are not necessarily causal ones, as he presents various graphs of two events that have a correlative, but clearly non-causal, relationship. For example the “number of people who drowned by falling into a swimming-pool correlates with [the] number of films Nicolas Cage appeared in [... the] per capital cheese consumption correlates with [the] number of people who died by becoming tangled in their bedsheets.” Martin Myers and Diego Pineda’s (2008) book Do Vaccines Cause That?! offers excellent data concerning the efficacy of vaccines and highlights how the false cause fallacy is committed by anti-vaccination advocates when trying to connect autism with vaccinations. The website logicalfallacies.info is an excellent compilation of various informal and formal fallacies, including the different variations of the false cause fallacy.
References
Federal Trade Commission. 2009. “Kellogg Settles FTC Charges that Ads for Frosted Mini-Wheats Were False.” Federal Trade Commission, December 15. https://www. ftc.gov/news-events/press-releases/2009/04/kellogg-settles-ftc-charges-ads-frosted- mini-wheats-were-false (accessed October 3, 2017).
Hurley, Patrick. 2015. A Concise Introduction to Logic. Stamford, CT: Cengage Learning.
Jacobson, S.W., and J.L. Jacobson. 2002. “Breastfeeding and IQ: Evaluation of the Socio-Environmental Confounders.” Acta Pediatric (91): 258-266.
McKay Illari, Phyllis, Frederica Russo, and Jon Williams. 2011. Causality in the Sciences. Oxford: Oxford University Press.
Morton, Sheila. 2014. Navigating Argument: A Guidebook to Academic Writing. Greeneville, TN: Tusculum College.
Myers, Martin, and Diego Pineda. 2008. Do Vaccines Cause That?!: A Guide for Evaluating Vaccine Safety Concerns. Galveston, TX: Immunizations for Public Health.
Vigen, Tyler. 2015. “Spurious Correlations.” http://www.tylervigen.com/spurious- correlations (accessed October 3, 2017).