On the technical functions of invalidity insurance

1. The mathematics of invalidity insurance are slightly more complicated than the mathematics of ordinary life insurance, the reason being that in the former we have to do simultaneously with several forces operating on various classes of lives. Also questions of consistency arise if, as is often the case, certain of the forces implied cannot be obtained from the observations in hand but must be borrowed from outside. It is therefore important to submit the system of formulas employed to a careful scrutiny with a view to detecting possible contradictions, and since the defects of certain formulas, not unlike those of human beings, have a tendency to become more marked at advanced ages, we shall pay particular attention to the behaviour of our formulas as the age tends to infinity. At the same time we shall be on the look out for possible simplifications of the comparatively heavy numerical work involved in these calculations.