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The problem of testing the null hypothesis of a common direction across several populations defined on the hypersphere arises frequently when we deal with directional data. We may consider the Analysis of Variance (ANOVA) for testing such hypotheses. However, for the Watson distribution, a commonly used distribution for modeling axial data, the ANOVA test is only valid for large concentrations. So we suggest to use alternative tests, such as bootstrap and permutation tests in ANOVA. Then, we investigate the performance of these tests for data from Watson populations defined on the hypersphere.

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Introduction: The study of eating behaviour should consider the presence of potential sources of bias, including social desirability. This is particularly relevant among students of Nutrition Sciences, since they have a higher risk of eating disorders. Objective: To analyse the effect of social desirability in the assessment of eating behaviour dimensions among nutrition students. Methods: In this cross-sectional study, we analysed data from 149 students of Nutrition Sciences. Participants completed a questionnaire assessing social desirability and eating behaviour dimensions (emotional, external and binge eating, flexible and rigid control, and eating self-efficacy). Results: Among males, social desirability had a negative association with binge eating, while among women it had a negative association with emotional, external and binge eating and a positive association with eating self-efficacy. In both subsamples, social desirability showed no significant association with any of the two types of dietary restraint (rigid and flexible control). Discussion: Overall, the association between social desirability and eating behaviour dimensions among students of Nutrition Sciences occurs in the same direction as found in students from other areas. However, alongside these similarities, there is a stronger association between social desirability and binge eating among male students of Nutrition Sciences. We hypothesize that this may be related with the different knowledge of students from different areas, and the way they perceive and face the treatment of eating disorders. Conclusion: Our study shows that social desirability should be considered while assessing eating behaviour among nutrition students, particularly when studying external eating, binge eating and eating self-efficacy. Moreover, when tailoring interventions to reduce the possible effects of eating behaviour on nutritionists and dieticians' practice, we should consider the influence of social desirability.