Intuitive Biostatistics

Each circle represents the spot where a rocket sent from Germany landed in London. Is there a pattern? It sure looks like it, but in fact the distribution is random, matching the distribution of the Poisson distribution. A chi-square test compares the expected and observed distributions  (RD Clarke, Journal of the Institute of Actuaries, vol. 72, 1946, p. 481). Tierny discusses psychological aspects of this example -- people are more likely to see patterns in random data when very stressed.