【正文】 y for a country or region over a year, using the total number of accidents (eventually of a particular type, such as fatal accidents), in order to pare this number with the oute of the year before. If sequences of accidents are given over several years, then trends in the developments can be detected and accident numbers predicted for following years. Once such a trend is established, then the value for the next year or years can be predicted, together with its error bounds. Deviations from a given trend can also be tested afterwards, and new actions planned. The most famous one is carried out by Smeed 1949. We will discuss this type of accident analysis in more detail later. 1. The application of the Chisquare test for interaction is generalised to higher order classifications. Foldvary and Lane (1974), in measuring the effect of pulsory wearing of seat belts, were among the first who applied the partitioning of the total Chisquare in values for the higher order interactions of fourway tables. 2. Tests are not restricted to overall effects, but Chisquare values can be deposed regarding subhypotheses within the model. Also in the twoway table, the total Chisquare can be deposed into interaction effects of part tables. The advantage of 1. and 2. over previous situations is, that large numbers of Chisquare tests on many interrelated (sub)tables and 9 9 corresponding Chisquares were replaced by one analysis with an exact portioning of one Chisquare. 3. More attention is put to parameter estimation. ., the partitioning of the Chisquare made it possible to test for linear or quadratic restraints on the rowparameters or for discontinuities in trends. 4. The unit of analysis is generalised from counts to weighted counts. This is especially advantageous for road safety analyses, where corrections for period of time, number of road users, number of locations or number of vehicle kilometres is often necessary. The last option is not found in many statistical packages. Andersen 1977 gives an example for road safety analysis in a twoway table. A puter programme WPM, developed for this type of analysis of multiway tables, is available at SWOV (see: De Leeuw and Oppe 1976). The accident analysis at this level is not explanatory. It tries to detect safety problems that need special attention. The basic information needed consists of accident numbers, to describe the total amount of unsafety, and exposure data to calculate risks and to find situations or (groups of) road users with a high level of risk. 4. Accident analysis for research purposes. Traffic safety research is concerned with the occurrence of accidents and their consequences. Therefore, one might say that the object of research is the accident. The researchers interest however is less focused at this final oute itself, but much more at the process that results (or does not result) in accidents. Therefore, it is better to regard the critical event in traffic as his object of study. One of the major problems in the study of the traffic process that results in accidents is, that the actual occurrence is hardly ever observed by the researcher. Investigating a traffic accident, he will try to reconstruct the event from indirect sources such as the information given by the road users involved, or by eyewitnesses, about the circumstances, the characteristics of the vehicles, the road and the drivers. As such this is not unique in science, there are more examples of an indirect study of the object of research. However, a second difficulty is, that the object of research cannot be evoked. Systematic research by means of controlled experiments is only possible for aspects of the problem, not for the problem itself. The bination of indirect observation and lack of systematic control make it very difficult for the investigator to detect which factors, under what circumstances cause an accident. Although the researcher is primarily interested in the process leading to accidents, he has almost exclusively information about the consequences, the product of it, the accident. Furthermore, the context of accidents is plicated. Generally speaking, the following aspects can be distinguished: Given the state of the traffic system, traffic volume and pos