Studies have shown that your ability to do maths is affected by what you believe. This is not particularly surprising, but it is frustrating. If the mathematical data goes against what you believe, you’re likely to dismiss the data and assume you misunderstood it. You’ll just keep believing what you did before. Ah yes, we are indeed creatures of bias.
Here is a great article about this (the one referred to in the video): http://www.motherjones.com/politics/2013/09/new-study-politics-makes-you-innumerate