Does eating chicken on the bone make children more violent?

That is the finding of a study published in the journal Eating Behaviors.  I have a lot of admiration for the study's lead author, Brian Winsink (I highly recommend his book Mindless Eating), but I'm going to have to file this one under "I don't believe it."  

I thought it was worth weighing in on since I'd seen the study reported on in several major media outlets.  I'm not saying that it isn't possible that eating chicken on the bone (vs. in chunks) doesn't cause aggression, I'm just saying that my priors are such that it will take a lot more than this to convince me.  

Why would we even expect that eating chicken on the bone causes aggression?  The authors suggest the following hypothesis:

Showing teeth is a common sign of aggression in the animal world. Dogs retract their lips and bare their teeth as a sign that they are willing to fight (Galac, & Knol, 1997). The baring of teeth may have similar meaning in intuitive human behavior

So, the authors ran an experiment.  

They took 12 children participating in a 4-H summer camp (yes, N=12), and split them in two groups, 6 in one and 6 in another.  On day 1, one group was fed chunks and the other group was fed chicken on the bone.  On day 2 , they reversed the foods fed to the groups.  On both days, the children's behavior was monitored and recorded.  For example, the children were asked to stay in a circle and the monitors counted the number of times the children left the circle (glad I didn't go to that 4-H camp!).  Paired t-tests were used to test whether behavior differed on the day the child got the bone vs. the chunk.

Here are some shortcomings of the study that make the results a bit hard to believe:

  • The small sample size.
  • Each child was only observed on 2 days (one with bone one with chunk).  However, on one day, the temperature was 97 degrees and on the other it was 76.  Lots of prior research has posited a link between temperature and aggression (hot = more aggressive).  Suppose you had a couple kids in a group with a tendency toward aggression who got assigned chunks on the colder (76 degree) day and bones on the hotter (97 degree) day?   The difference in their behavior may be due to temperature not bones.  It would be nice to see tests for within-day differences in bone vs. chunk.  If one had a large sample with random assignment to treatments on multiple days this wouldn't be as much of a concern, but it certainly is here.
  • Children assigned to the same group sat at the same table together.  This may have produced some sort of group dynamic.  Suppose, for example, the kids assigned to bone started arguing at the table and the conflict spilled over to the playground.  The current study cannot separate group-day effects from the treatment effect (bone vs. chunk).
  • Given the small sample size, really all it takes is one or two kids changing behavior from day 1 to day 2.  How do we know this wasn't due to something at home that carried over to the camp?  With such a small number of observations, I don't know why the authors didn't just report the entire data set in one table.  That way, we could see whether the difference was from a small increase in aggression of every child or a large increase in aggression of 1 o 2 kids.  
  • The counselors who kept the kids in the circle and who rated behavior were "blind" as to the treatment and control groups each day. That's good.  However, the study doesn't tell us whether the people who subsequently watched the videos and rated behavior were also blinded.
  • Maybe the effect exists but for very different reasons than those hypothesized in the paper.  I've already mentioned a temperature explanation.  What if children like to eat chicken on the bones more than they do in chunks (my kids certainly do).  Maybe they get more excited and rambunctious when they get a "treat" or something they like, which the current authors attribute to "aggression."  Perhaps when the counselors give the kids a food that the kids perceive as more generous or benevolent, it signals to the kids that the counselors will subsequently be more permissive.  To control for this, you'd want some treatments where the bone-in food was less desirable than the boneless food.

At the end of their article, the authors suggest a number of lines of additional research that are interesting and worthwhile.  But, they also give some advice.   The authors suggest

school cafeterias may reconsider the types of food they serve if it is known that there are behavioral advantages to serving food in bite-size pieces


it may not be wise to serve young children chicken wings shortly before bedtime, or to serve steak and corn-on-the-cobb in the company of dinner guests.

That may be good advice in general, but this study alone is insufficient reason to re-engineer lunch lines or dinner plans in an effort to reduce child aggression.