Friday, June 25, 2010

Colds and causality

Over the past two weeks, I had a bit of a cold.  At various points I was coughing, I had a sore throat, I had a stuffed nose, my sinuses hurt, I was tired, and so on.  I'm better now.  If I were still living on campus I probably wouldn't have done anything about it except maybe take some dayquil or something.  But since I'm home right now, my parents are giving me the usual treatment.

My mom has been giving me some traditional medicine consisting of tea and honey.  It's some sort of special tea that tastes like licorice, and some kind of special honey that is supposedly good for colds.  I'm not sure I believe that, but I like tea and honey anyway.  The honey is sweet and dissolves well in tea.  The tea is a bit too much licorice for my taste, but it's good too.

My friend who is in nursing said that if it makes me happier, it probably boosts my immune system.  But if that is the mechanism at work, then surely any kind of tea and honey would do.  I'd probably prefer chamomile tea, and it could be a cheaper honey.  Or I could do without any honey at all, because I like dark and bitter tea, which may or may not be a metaphor for my soul.

My dad, who has a somewhat different philosophy about medicine, bought me some Nyquil.

The conversations between my mom and dad on the subject of my cold were probably hilarious.  But you, my readers, will never know, since I'm not in the habit of publishing private conversations on the internet.

This is all to say that I'm not that highly principled when it comes to taking medicine.  Maybe it's because I'm apathetic about my health.  Or because it's not that expensive and I'm not paying for it myself.  Or maybe it's because, when it comes down to it, I'm don't personally know of any scientific research that says Nyquil probably works better than these particular kinds of traditional medicine.

I am somewhat more principled when it comes to attributing causes.

My mother would like to credit my recovery to the tea and honey.   The thing is, colds usually go away on their own with time and rest.  This cold has been slowly declining over the past two weeks since before I started drinking the tea.  I'm just going to keep drinking the tea until it goes away entirely, at which point my mother will credit the tea.

The reasoning goes that I drank special tea with special honey, and now I'm better.  The reasoning applies equally well to any other number of ordinary things I did in the past two weeks.  Seriously, how else would we expect it to happen?  Would I drink the tea after I get better?  Would I just never get better?

Causality is one of the most difficult things to prove.  Without getting too philosophical about it, causality means that if I change factor A (ie drinking tea) independently of anything else, then factor B (ie recovery from the cold) will be different.  To even begin to prove causality, I need two data points, one where I drink tea and one where I don't.  And since a lot of random factors are involved, we actually need a lot more than two data points in order to average out the results.

Furthermore, the tea drinking factor really does need to be independent of anything else.  If the tea is always accompanied by Nyquil, that will completely compromise the evidence.  More subtly, if the tea is always accompanied by my belief that I am drinking special tea that will help me, then this too will compromise the evidence.  That's why we need placebo-controlled studies, to separate out the effects of treatment from the effects of believing in the treatment.  If only the belief suffices, I might as well be drinking chamomile tea.

I'll say it again: causality is extremely difficult to prove.  In the face of this difficulty, all I have is one data point.  One measly data point.  I'll take the tea because I like tea, but I refuse to interpret the "results" as evidence of anything whatsoever.  Same goes for the Nyquil.

Other posts in this mini-series:
Colds and Causality
Women and Causality
Responsibility and Causality
Nature/nurture and Causality 
Physics and Causality 
Math and Causality


Larry Hamelin said...

I like dark and bitter tea, which may or may not be a metaphor for my soul.

Take it from someone who really does have a dark and bitter soul: it's definitely not a metaphor for yours.

miller said...

Haha, I just like to joke that it is.

Jeffrey Ellis said...

I think the coincidental correlation between a "treatment" and a recovery from a health problem (that would have happened anyway) is exactly what keeps people going back to chiropractors.