Catálogo de publicaciones - libros

Evidence shows that mutations along some genomes do not all occur independently. This paper introduces statistical methodology for testing the assumption of independence of the substitution processes acting at two different positions. We consider specific pairs of sites along a genome of interest. For each pair, we focus on the distribution of double mutations away from the consensus (i.e., the most frequent configuration) conditioning on the total number of sequences and on the consensus pair. The resulting test statistic is applicable to general contingency tables that have an arbitrary number of rows and columns.

The Swiss Federal Veterinary Office (SFVO) applies risk analysis methods in the fields of animal disease control and food safety. Analysis results are used to formulate import regulations for animals and goods, to check the effectiveness of control measures, and to set up monitoring programmes for animal diseases and food contamination. The assessment of the potential health risks to the population from consuming milk and dairy products contaminated with zoonotic agents is used to demonstrate the steps and the advantages of a qualitative risk assessment. The probability of contamination occurring in raw milk, retail milk, and 12 milk products was investigated. The products posing the greatest risk were raw milk and fresh and soft cheeses whereas the risk from pasteurised milk, cream, butter, and hard cheese was seen to be negligible. Based on these results, the first risk-based monitoring of milk products was introduced in Switzerland in 2002. The initial phase of a risk analysis is a qualitative process. Often, while the risk network is being established, it is realised that the required data are unavailable or that data quality is insufficient. Qualitative evaluation of expert opinion is easier than quantitative evaluation. However, assigning risks to qualitative categories is done subjectively and there is no standardised method. Usually the information provided by qualitative assessments is adequate for risk managers for decision making. Management measures in public health are often ‘yes’ or ‘no’ decisions. Risk communication between risk managers and stakeholders is simplified when the results of a qualitative assessment are available.

Risk analysis can be performed following either a quantitative or a qualitative approach. Both methodologies are linked to the same theoretical rules. Once the potential hazard has been identified, the qualitative risk assessment is carried out by combining the probabilities of occurrences of the events (emission and exposition) in the presence of a hazard, and its consequences. The probability of an event can be evaluated by combining the probabilities of the different parameters. Within the frame of global expertise, the necessity of realizing collegial risk evaluations, sometimes when only few data are available and within a short amount of time, leads us to work on a standardised method for a qualitative approach. The process of global qualitative risk appreciation is completed by adding support to the rationalisation of the estimation step. It has been proposed that each parameter be evaluated with the help of all available information and that an evaluation of the probability of occurrence of each of these can be realized individually to yield a given level of probability (null, negligible, low, moderate, high) or an interval between two levels (for example: ‘negligible to low’). The combination of probabilities and of intervals was carried out using a table that was tested and evaluated through the following risk assessment: qualitative risk evaluations of the transmission of Q fever to humans in France. Both the advantages and the limitation of this approach are also presented.