Thursday, April 26, 2007

Living rationally under the volcano?

I am interested in Arcidiacono et al (2007) which deals with whether forward-looking ‘rational addiction’ models best explain patterns of smoking among late middle-aged men. The suggestion is that one cannot observe whether decisions by young people to smoke or drink are consistent with rationally thinking through the health consequences of smoking or not.

As a general rule relatively few adverse heath effects occur in the first half of life. Young males who smoke, according to Hodgson (1992), have the same cumulative probability of surviving to age 35 as non-smokers. At age 45 (age 65, age 85 respectively) the corresponding ratio of the cumulative probabilities is 1.02 (1.18, 2.11 respectively) so that a smoker faces a 2% higher cumulative probability of being dead than a non-smoker at age 65, 18% at age 65 and 211% higher at age 85.

This evidence surprises me. The impression I had gained from other studies was that the smoking risks over middle ages were larger than these. For example, Doll et al (2004) examine smoking behavior of 34,439 male British doctors over a 50-year period and found that long-term smokers died 10 years younger than non-smokers – that is possibly consistent with the Hodgson data. But among men born around 1920, Doll et al found that prolonged smoking from early adult life tripled mortality to 43 per cent among smokers compared to 15 per cent among non-smokers between ages 35-69 – this seems much larger than the increased cumulative probabilities cited above. Or am I missing something? Moreover, according to Doll et al cessation at age 50 halved the mortality hazard and cessation at age 30 avoided most of it. There are huge public health gains from getting people to quit cigarettes.

According to the Hodgson claims, the disease consequences of smoking only really bite in the second-half of a male’s life. This means that a young male may choose to smoke rationally with complete account taken of future harmful consequences (without relying on hypotheses of above-average discount rates or impulsiveness levels) simply because, even with moderate discount rates, the cost of a premature death in the second half of their life has low present value.

In fact, examining data on young males won’t tell you if they are rationally choosing to smoke with a reasonable discount rate or behaving irrationally and myopically by enjoying the future now without regard to future consequences. In short you cannot test the ‘rational addiction’ hypothesis of Becker and Murphy (1988) using data on young males.

The Arcidiacono et al (2007) paper itself examines whether late middle-aged males – who do face significant extra mortality risks from smoking (and drinking). Do these males update their consumption behaviour in the face of adverse health shocks? Do they display rational forward-looking behaviour or is their behaviour myopic? They find that older males are rational addicts with moderately high discount rates who fully anticipate the risks associated with heavy smoking and drinking even though smoking, while young, can make sense at moderate discount rates. Myopic models in this setting imply much higher levels of drinking and smoking than do occur. Rational addiction models imply lower levels of these consumptions because individuals account for their future health costs. This is hardly surprising given that the conventional wisdom supposes that older people are more mature and have lower discount rates than adolescents. They will also be observing the health consequences of smoking.

Smoking when young does pose particular neurobiological costs as I have suggested before that are real even if they are not necessarily fatal. Also those who begin smoking or drinking when they are young are more likely to remain addicted to cigarettes or to become alcoholics than those who start later in life. It is thus costly to smoke when you are young even though, according to Arcidiacno (2007) it may be rational to smoke if you don’t mind smelling like a compost heap throughout your life, and don’t worry too much about dying a decent way down the track because you discount the future at a plausible rate.

I think this is an interesting viewpoint. In the past I have argued that young people behave irrationally because they have high discount rates – they are impulsive and so on. The argument constructed by Arcidiacono (2007) suggests that this issue is unlikely to be resolved by appealing to evidence and that observationally it doesn’t matter much because of the life-profile of health risks.


Anonymous said...

A medical doctor friend and I used to smoke heavily in our twenties. I recall having the discussion that smoking at this age is not likely to have an affect on our health if we stop at 35, which we did.

Of course, we lacked fitness in our 20's. So much so that after returning to UQ a non-smoker the once massive exhausting hills on campus had completely disappeared.

(ps, I'm very upset with the word verification i got for this post:
typical kalimna antics)

hc said...

Rabee, I am glad you stopped. Its an interesting argument though that all the 'rational addiction' papers test young people where the hypothesis probably can't be tested.

I actually think that you and your friend were the exceptions. Other evidence suggests stronglg that youing people do have high discount rates. But, at least in terms of smoking behaviour, we will never know.

Anonymous said...

You don't find too much angst about over 55 yo cannabis users, extasy users, ice users, heroin users. Mainly I spose cos you don't find that many users over 55.

To some extent the nature of the drugs and their effects appeal to certain age groups.

I have no figures at all but might it be that older users are better at risk management and therefore better at not being caught?

A big part of tobacco use damage, other than cancer, can be reversed can be reduced after a few years of abstinence.

And a irrelevant and iritatiing anecdote. My neighbour gave up a lifetime, since 15yo, of chain smoking when she was 89. She died last year at 92 from non smoking related causes.

hc said...

fxh, I think about half of lung cancer sufferers are ex-smokers.

One puzzle about hard drug use was that it is concentrated at the start of life rather than the end. Why wouldn't you want to bliss out at age 85. If you mistake and OD you only lose a few expected years of life.

I have heard some criticise the rational addiction outcome for this view. The analysis presented in the post rationalises this paradox.