We consider statistical analysis of multiple answers in a questionna- ire. We propose a new method of calculating simultaneous confidence regions. In a communication presented at the European Academy of Allergy and Clinical Immunology the authors (Borowicz et al. (2009)) reported the proportions of respondents which gave one of three po- ssible exclusive answers in a questionnaire concerning the role of vo- luntary health insurance. There were three possible answers. Apart from percentages of answers confidence intervals of every single an- swer have been reported. Unfortunately inference about the popula- tion based on such intervals may lead to imprecise conclusions. The inference about the respective population suffering from allergy and asthma proportions requires the construction of two-dimensional confidence region. We propose the use of a simultaneous confidence intervals to inference about true population proportions. Most of our attention is given to the case of three possible answers but the results may be generalized to any questionnaire with more than two excluding answers.
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In the paper, the formerly introduced spherical multivariate tests are coupled with procedures for selecting the relevant variables. These procedures work in such a way that a non-relevant set of variables is chosen with the probability of significance \alfa, at most. Furthermore, a new method of the calculation of linear principal-component scores is presented, which is based only on the within-sample covariances and yields, nevertheless, a level-\alfa test in each case. This method enables us to determine novel multivariate confidence regions of the unknown mean vector. The statistical procedures are demonstrated by a neurological example.
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