BMI on Craigslist

There was a post, w4m, on Craigslist. In it, the author listed that she was 170lbs (I'm not sure if she posted her height), and was looking for someone who's single, under 30, and has no kids.

As tends to happen on any anonymous internet board, someone replied that she was picky. Someone else posted that the requires were not particular at all (which I agree with). Then two other people chimed in to say that 170 is "pretty big" unless "you must be like 7'8?", and that 1"70 is large unless you are REALLY tall".

I was curious, so I looked up the Body Mass Index (BMI), which has the following form:

BMI = (weight * C) / height^2

where C is a constant adjusting for the units.

A BMI in the normal range means it is between 18.5 and 25, with 22 being the average. This gives a height range of [69.14,80.37] inches, with an average of 73.70 inches. The average height for American females above twenty is 64 inches, which results in a BMI of 29.18, firmly in the overweight category and bordering on obese. There is a 3.8% chance of her being within the normal range, as 96.2% of American females are shorter than 5'9.

So, while the Craigslist posters were harsh, they were also, unfortunately, correct.

On a different note, the section of the US female population least likely to be overweight is (sterotypically) the Asian/Pacific-Islander (25.2% overweight/obese). The next least likely (surprisingly) are those with a graduate degree (29.2%). Interesting.


  1. guess that puts you 2/3 of the way to being the least likely person in the U.S. to be overweight...

  2. Assuming the statistics are independent - that is, my age has nothing to do with my race which has nothing to do with my education - I actually have a very low chance of being overweight:

    Male 18-24 y.o.: 41.5% overweight
    Male Asian: 35.2% overweight
    Male Grad: 53.7% overweight

    To get the joint probability (with the assumption above), simply multiply:

    .415 * .352 * .537 = 0.07844496

    So given someone who is male, 18-24, Asian, and working on/have a graduate degree, there's only 7.8% chance of them being overweight. Pretty good, eh?

  3. Sigh. Isn't the probability of you being an overweight male Asian or male grad somehow dependent of you being a male? I don't think you can simply apply the "and" rule and multiply all three probabilities together.

    I'm kind of curious why you write so much about craigslist posts. I feel like comments sections on public forums are basically just outlets for people to vent their frustrations and insecurities on others. Reading them is bound to expose you to people's pettiness more than anything truly informative.