In April 1940, while visiting in-laws in Copenhagen, Kerrich was caught up in the Nazi invasion[3] and interned in Hald Ege, Viborg, Midtjylland.
While there he conducted simple experiments using coins and ping-pong balls to demonstrate the empirical validity of a number of fundamental laws of probability.
On his release after the end of the Second World War, Kerrich published an account of his experiments in a short book entitled An Experimental Introduction to the Theory of Probability.
[5] Kerrich and Christensen also performed experiments using a "biased coin", made from a wooden disk partly coated in lead, to show that it too tended towards a stable asymptotic state with probability of approximately 70 percent.
In addition, the pair used urn problems involving drawing colored ping-pong balls from a box to demonstrate Bayes's theorem.