We have printed the foregoing paper by Mr. Munden as submitted because we think that the detailed analysis will be of interest to all who have interests in the field of motor insurance rating. Of necessity, the data does not lend itself to analysis with respect to some of the known variables and we are conscious that some of the conclusions are controversial; some factors have also emerged from the discussions within ASTIN on motor insurance and it is therefore hoped that the following comments will be of value in relation to the paper.

It is of the utmost importance that a clear distinction is drawn between the concept of accident proneness and the heterogeneity shown from observations of claim frequencies under insurance policies. As the discussion at La Baule brought out, the first conclusion to be derived when a compound Poisson distribution emerged is that there is a degree of heterogeneity in the data. This might be due to differences in accident probabilities of the underlying risks, but it could be due, for example, to different exposures of similar risks. Lanteli's paper to the Rättvik colloquium showed a substantial variation of claims experience with annual mileage and thus without an analysis controlled with respect to mileage the conclusion that a proneness factor is solely involved must be suspect.