Mean, Median, Bill Gates and Prof. Julia

The first module I am teaching at KHI is biostatistics for the 3rd year physiotherapy students.  Like the American students, very few of them enjoy it but they seem to be tolerating my teaching and teaching style and we are getting used to each other.  Last week, I was teaching about measures of central tendency and talking about choosing the right measure to match the data and the distribution.  In describing the choice of median over mean as a measure I asked the students to think of a measure that produce a skewed distribution.  Since they could not, I decided to give them the tried and true example of income.  I asked them who the richest person they could think of was and they all easily answered Bill Gates (he visited Rwanda and his foundation funds projects here).  I then asked them how much income they thought he generated each year and his net worth they guessed around 1 million dollars of income and 6 Billion worth (underestimate but who knew??).  I drew Bil Gates on a graph on the board and then I asked them what they thought my income might be and where the "average" American income would sit on my graph.  They thought that I must earn close to Bill Gates because, like him, I come from THAT country.  I proceeded to draw on the board a graph that looks like this one:

Then I showed them that my income while quite generous by both US and, of course, Rwandan standards is not pulling the distribution as much as Bill Gates.  It was surprising for them to learn.

They seemed to understand median as a measure and more importantly, they seemed genuinely surprised that Bill Gates' current worth is in the millions while Prof. Julia's current worth...well...its just not worth discussing.  They learned about skewed distributions and I learned about their skewed beliefs.