Category Archives: Bias

Photo of two rocks, larger 25 times heavier than smaller.

Drop two rocks

On your next walk pick up two rocks which vary in size; drop them simultaneously. Aristotle, in 350 BCE, stated that the rocks would fall with a speed directly proportional to their weight.


The large rock on the dinner plate is 25 times heavier than the small one. I dropped them from eye level. If Aristotle was correct, the large one should have hit the   ground about the time the small one passed my lips. Instead, they fell at the same speed and hit the ground at the same time. Apparently Aristotle never did this simple test; nor did anyone else until Galileo presented a thought experiment in 1628. For almost 2000 years the entire community of natural philosophers accepted and propagated this delusion. For good reason, this is how pre-scientific natural philosophy worked. Starting with a given set of truths, the philosopher used deductive reasoning to arrive at new truths. Aristotle’s reasoning was sound, the starting truths were wrong. Once a truth– it stayed a truth

Bias: we all have it.
In 11 of the past 20 years the Gallup poll has asked the following question:
Which of the following statements comes closest to your views on the origin and development of human beings –

  • human beings have developed over millions of years from less advanced forms of life, but God guided this process,                        (blue line,      mean =  37%)
  • human beings have developed over millions of years from less advanced forms of life, but God had no part in this process,         (orange line,  mean = 12%)
  • God created human beings pretty much in their present form at one time within the last 10,000 years or so?                                             (grey line,      mean = 45%)
  • No opinion                                                                     (yellow line,   mean =   6%)

GallopHumanOriginThe groups have maintained the same rank order in every poll for 20 years.  A Newsweek poll in 2007 had similar values and the same rank order.
The rocks I dropped as part of the Galileo story are millions of years old.  This information should eliminate the top line in the chart  and raise questions about the second line, but it hasn’t and it won’t for a very long time. The 80% of the population in the top two lines include teachers, doctors, sales people, business owners, and executives who routinely make valid data-based decisions on other issues. They are friends and neighbors. It is critical to understand that we each have beliefs which bias our data decisions.

If an analyst has made a choice, he has also made a value judgment – Jonathan Koomey