The Consequences of Risky Behaviors | 91
Some suggestive evidence indicates that this secondhand smoke, in addition to causing tobacco-related illnesses in children, also depresses their cognitive performance. A longitudinal study using pregnancies occurring between 1960 and 1967 in California found a significant association between parental smoking and scores on two of four cognitive skills tests, which persisted even after the inclusion of controls for parental income, education, and prenatal smoking (Bauman, Flewelling, and LaPrelle 1991). The mechanism behind this relationship, however, remains unclear. We do not know, for example, whether secondhand smoke deprives children’s brains of oxygen, whether it is associated illnesses such as respiratory infections that impair cognitive performance, or whether parents who smoke tend to be less effective in fostering the cognitive development of their children. We do know that parental smoking—at least the smoking of mothers— does have a biological impact on children while they are still in the womb. The evidence comes from both randomized control trials and the natural experiments that often result from changes in the price of cigarettes. In one trial in the United States, pregnant smokers were randomized into a group that received standard prenatal care or another group that also received counseling to quit smoking during their pregnancies. To estimate the impact of maternal smoking on birth outcomes from this experiment, we can look at the ratio of the direct impact of the counseling on birth outcomes to the impact of the counseling on maternal smoking (the Wald estimator in econometrics). A study that analyzed this experiment’s data in this way found a smoking effect of 400 grams in birth weight, or nearly 0.9 of a pound (Permutt and Hebel 1989). Given the evidence on the detrimental impact of low birth weight on outcomes later in life, such as educational attainment and wages (Black, Devereux, and Salvanes 2007; Oreopoulos and others 2008; Royer 2009), this health discrepancy that emerges among children of smokers and nonsmokers very early in life could translate into permanent differences in terms of adult health and income. Outside of the deliberate manipulation of experiments, we need to rely on forces that influence whether pregnant women smoke but that do not affect birth outcomes directly. Changes in cigarette prices can often do this, since they tend to follow a change in an excise tax specific to cigarettes. In another study, researchers used the census of all births in the United States, which records the smoking status of the mother, and examined what happened to maternal smoking and birth outcomes after a change in states’ excise taxes on cigarettes (Evans and Ringel 1999). They found a similar impact on birth weight, namely, a detrimental smoking effect of 353 to 594 grams.
Secondhand smoke and coworkers Since smokers generally do not limit their habit to the home, smoking could also affect their coworkers if nothing prevents exposure to second-