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First Comes Love, Then Comes Obesity…

July 7th, 2009 · 13 Comments
Econ 101 · Incentives

I’ve believed for a long time now that there is a hint of truth in every joke…and never did I learn that more than this weekend. Word to the wise: don’t joke about somebody’s girlfriend getting fat because she’s in a relationship. Just don’t. Even if it makes perfect sense. Luckily, the response I got was “Funny you say that. Here, take a look at this article..” *friend goes into bathroom to retrieve magazine* Oh boys…

The article that my friend was referring to is from Time magazine and is titled “First Comes Love, Then Comes Obesity?” (hence the title of this post). The article basically confirmed some of my worst fears about human nature. A few highlights:

  • Within a few short years of getting hitched, married individuals are twice as likely to become obese as are people who are merely dating.
  • Not only are married people more likely to become obese than those who are just dating, but young people who move in with a boyfriend or girlfriend tend to pack on the pounds too.
  • The study notes that unmarried women who have been living with their sweeties for five years or less run a 63% increased risk of obesity. What about unmarried men? On average, they have no increased risk during cohabitation.

Now, this study was published in a journal called Obesity, so I am unclear as to the level of analytical rigor in its article review process. (I don’t say that for any reason other than I am not familiar with said journal.) Since marriage/cohabitation/whatever is a choice, I would hope that the study at least tried to correct for the selection bias in the control (non-attached) versus the experimental (attached) group. In other words, there could be something about the people who chose to live together and/or get married that is also causing them to get fatter. If this is the case, these people would have gotten fatter regardless of whether they were in relationships. Therefore, the relationships themselves could be taking the blame for something they they didn’t actually cause. (For a refresher course on correlation versus causation, see here.)

The article gives several logistical hypotheses for the findings- increased importance of mealtime, for example. That said, my brain has been carefully trained to look for incentives everywhere. Unfortunately, this fact causes me to come up with such socially-questionable explanations as “marriage creates bad incentives.” I’m such a romantic…but I really do have a valid point. When you marry someone, you are (theoretically) contracting on staying with them forever, no matter what. Given that your spouse is stuck with you, what incentive do you have to, oh I don’t know, go to the gym, not sit on the couch and eat potato chips (mmmm, potato chips), etc? People (usually men, in my experience) seem shocked when their partners don’t act the same after they get married than before, but why would they when the incentives are so different?

This is the classic moral hazard problem. Moral hazard refers to the concept that a person behaves differently when she is insulated from the risk of her actions. The example usually used when talking about moral hazard is insurance- people generally drive in more risky ways when they have car insurance than they would if they weren’t insured, since they don’t have to bear the full cost of getting in an accident. (Before you object, consider that a lot of the change in behavior could be happening at a subconscious level.) Even if the spouses really care about each other, the lack of dumping potential results in a form of insurance that is likely to change behavior.

Luckily, there are factors that serve to mitigate the change in behavior. Just as there are non-financial reasons (pain, inconvenience, etc.) to not get in a car accident, one would hope that there are non-mating reasons (self-respect and health come to mind) for not becoming a fatass. I think the study described above is interesting in that, other than stating the anecdotally obvious, it gives some insight into the relative importance of the reasons for taking care of one’s self.

So why does the study report that even unmarried couples seem to exhibit the same type of incentive problem? If you’re not married, there is no legal string forcing another person to put up with you and all of your, um, personal growth, if you will. Yet the moral hazard still exists. Some possible explanations:

  • There are other logistical factors, such as cohabitation or children, that make separation difficult in the same way that marriage would.
  • The partner doesn’t properly account for sunk costs and will stick around because (s)he “has already invested so much in the relationship.” (In case you’ve forgotten, sunk costs are those investments that you’ve made that you can’t get back regardless of your future choices. Therefore, sunk costs shouldn’t affect your future decision-making process, but most people find them hard to ignore.)

In case you’re curious, I’m not in reality *quite* as cynical as I seem here, but I’m close, since people are, well, human and imperfect. A few days ago I had an ex-boyfriend promise that if I ever got married he would be a bridesmaid…complete with dress and all. I’m not sure whether this speaks more to my marriage prospects or to his tolerance for humiliation.

I figured that Jessica Hagy would have a nice card on the topic, but surprisingly this was the closest I could find:

It took me a second to get it, but it’s sort of amazing. The best part about this, in my opinion, is that the caption is “Here’s an ugly model.” 🙂

Tags: Econ 101 · Incentives

13 responses so far ↓

  • 1 Steve Davis // Jul 7, 2009 at 4:09 pm

    I especially enjoy that the Google ads that showed up are mostly about losing weight. (And one advertising the Ford “Escape” ????)

  • 2 Barbara Horne // Jul 7, 2009 at 4:12 pm

    I love the Supply and Demand curves.

  • 3 Court // Jul 7, 2009 at 5:08 pm

    Hah, so true. The comic is amazing btw.

  • 4 Larry // Jul 7, 2009 at 5:21 pm

    Love it! This is a great article 🙂

  • 5 econgirl // Jul 7, 2009 at 5:28 pm

    @ Steve: I would like to state for the record that the Google ads are mainly there for humor value. 🙂

  • 6 PeterM // Jul 7, 2009 at 7:38 pm

    Did the study account for the influence of having children? If there are children in the picture (and remember a fair number of children are raised by unmarried couples as well as married ones) one gains weight in two ways. First, when a kid is young, you stop doing many activities. Dancing at a club? Jogging? Forget it. Second, as to females, there’s pregnancy weight gain. Third, when people have kids, they often stop smoking — which is about an automatic 10 pound weight gain. I don’t know how reliable this data is, but I read that “1.25 million babies (one third of all births) are born each year in the U.S. to unmarried parents. Many people just assume these babies are born to single moms, when in fact 41% of these births are to unmarried cohabitating couples.” My experience is that one spends a lot more time being sedentary.

    Gee, I thought sunk costs were what happened to one’s rear end from too much grocery consumption. Or are those sinking costs?

  • 7 PeterM // Jul 7, 2009 at 7:40 pm

    Make that “three ways.” I’d be a better proofreader if you paid your commenters for lucid, logical comments.

  • 8 Nathan // Jul 7, 2009 at 8:28 pm

    lol ur so funny

  • 9 Amanda // Jul 7, 2009 at 9:18 pm

    Well, I think it’s common understanding that people tend to put less time into their appearances the more secure a relationship becomes. Looks make for great bait, but I’d like to think the most marriages are built on more than that!

    Love the blog, by the way.

  • 10 Dan L // Jul 7, 2009 at 10:58 pm

    I agree with PeterM. If the study did not consider the effects of having children, then it’s not worth the paper it’s written on. It should also normalize for age, by the way.

    In any case, I doubt anyone is surprised by the study’s conclusion. Single people have greater incentive to look good than attached/married people. Does anyone seriously doubt this? I suppose that quantitatively measuring the effect of this incentive is mildly interesting.

    Here’s satirical “economic” explanation for the effect of marriage on obesity: Cohabitation yields savings that can be spent on junk food, and getting married saves extra money on taxes!

  • 11 Ignas // Jul 11, 2009 at 12:54 am

    Interesting stuff.

    This adds to the lore that men expect their wifes to stay the same way forever and are unpleasantly surprised to find that they don’t. While women expect their husbands to change (grow up!) and are shocked to realise that, actually, most of them don’t.

  • 12 Ben Ho // Jul 17, 2009 at 12:24 am

    “so I am unclear as to the level of analytical rigor in its article review process. (I don’t say that for any reason other than I am not familiar with said journal.) ”

    I think that’s a fair assumption. I’ve learned from the few times I actually looked up epidemological articles that even top medical journals like JAMA and teh New England Journal will publish based on correlation alone. Which is part of why most of these medical studies are so often overturned.

    I am willling to bet that that paper in particular did not control for selection. At least that was what I assumed when reading the article from my bathroom.

    Still, I’m sure the effect is real. My wife was particularly troubled by the finding though.

  • 13 Ankit Ashok // Jan 17, 2010 at 12:02 am

    Was the study normalized for age?
    Also one huge incentive to stay fit would be peer pressure. No one wants to be the fat-one in the group.

    And, rofl on the supply-demand Indexed pic.

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