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| Author(s): |
Nilda Doris Montes Villanueva
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia de Alimentos |
| Defense date: | 2003-07-31 |
| Examining board members: |
Maria Aparecida Azevedo Pereira da Silva;
Armando Mario Infante;
Eliete Vaz de Faria;
Jose Herman Berhens;
Luciane Vieira Garcia
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| Advisor: | Maria Aparecida Azevedo Pereira da Silva; Ademir José Petenate |
| Abstract | |
In sensory tests, the basie statistieal toei for analyzing data is almost invariably some sort of analysis of variance models. These models presuppose that the experimental responses are: i) independent, ii) normally distributed, iii) homoscedastie (have equal varianees) and, iv) seores are on the same scale of measurement (additivity). The main problems arising from the analysis of sensory data using ANOVA models are related to the last two assumptions. Homogeneity of error variance is not assured, espeeially as there are at least two potential sources of heterogeneity: treatments and assessors. On the other hand, the additivity could be violated if one assessor used a eonsistently larger (or smaller) portion of the scale range, scoring more (or less) expansively than other assessors to express his opinion of the produet. The individual way in whieh eaeh panelist uses the scale to evaluate the produets is known as the differential expansiveness of seoring between assessors. 80th the laek of homogeneity of the variances and the non-additivity of the model, result in serious consequenees in obtaining a true levei of significance for the effect of the treatments and may adversely affeet the eomparison of treatment means. The non-additivity can seriously affeet and possible invalidate the analysis of variance and the interpretation of the results that it provides. In consumer tests, traditional scales sueh as the nine-point hedonie scale frequently present the following problems: i) they do not satisfy the statistical assumptions of independenee, normalityand homoscedastieity required by ANOVA models; ii) they give little freedom to the individuais to express their perceptions, due to the limited number of categories; iii) they induce numerical and contextual effects in the judgments by the panelists and, iv) the difference between numerical values associated with the categories do not reflect equivalent differenees in perception. Of the methodologies used in sensory tests with consumers, the 9-point hedonie scale is undoubtedly the most widely used. However, considering the previously mentioned problem, there is a need to investigate alternative scales providing better performanee than the traditional hedonie scale, both when the data are analyzed by ANOVA models and multivariate methods such as the Internal Preference Map - MDPREF. In general the objective of this research was to investigate the performance of two alternative scales in consumer studies, these being the self-adjusting scale and the hybrid hedonic scale, comparing them with traditional affective methods such as the ranking scale and the 9-point hedonic scale. With this objective three experiments were carried out as follows: The first experiment was carried out with the objective of evaluating the performance of the self-adjusting scale as compared to the 9-point hedonic scale and ranking scale under real consumer test conditions, using the following criteria: i) differential expansiveness between assessors, ii) discriminating power and, iii) compliance of the data collected by each scale with the ANOVA assumptions. Three commercial brands of candy were evaluated by 288 consumers. The results obtained from the 9-point hedonic and self-adjusting scales were analyzed by ANOVA and those of the ranking test by Friedman's test. The values for pFsample, pFassessor and QMerror provided by ANOV A for each scale, were used respectively to evaluate the discriminating power, the expansiveness of scoring between assessors and the data variability. Tukey's test was also applied to analyze the discriminating power of each scale. Normal probability plots, Kolmogorov-Smirnov test and coefficients of skewness and kurtosis checked data normality. Homoscedasticity was evaluated by scatter plots and the Levene test. The results showed that the self-adjusting scale was effective to deal with differential assessor expansiveness and produced homogeneous variances, however the residuais showed moderate deviations from normality. The 9-point hedonic scale showed problems with heteroscedasticity. Rank and the self-adjusting scales showed the highest and the lowest discriminating powers, respectively. Despite the problems detected, the three scales presented the same tendencies for preference amongst the products tested. The second experiment was carried out with the objective of evaluating the performance of the hybrid hedonic scale in consumer studies, comparing it with the 9point hedonic, the self-adjusting and the ranking scales, using the following criteria: i) variability of sensory response, ii) discriminative power, iii) data adequacy to the assumptions of ANOVA models and, iv) ease of use. Eighty consumers, divided into four groups of 20 individuais each, evaluated tive brands of orange juice. Ali the individuais evaluated ali the samples using ali the scales, in 4 distinct tasting sessions. A 4 x 4 Latin square design was used to control the effect of the order of presentation of the scales and evaluate their ease of use without biases. For each scale the presentation order and carry-over were balanced. The results obtained using the traditional hedonic, hybrid hedonic and self-adjusting scales were evaluated using ANOVA. Data normality was evaluated using the Shapiro-Wilks test, homoscedasticity by the Brown-Forsythe's test and the Tukey's one degree of freedom test for non-additivity. The values for pFsample, pFassessor and QMerror, provided by ANOVA for each scale, were used respectively to evaluate discriminating power, expansiveness between assessors and data variability. The REGWF test was also applied to analyze the discriminative power of each scale. The results obtained from the ranking test were evaluated by Friedman's test and the ease of use of the scales by the Cochran-Mantel-Haenszel tests. The results indicated the superiority of the hybrid hedonic scale as compared to the structured hedonic and self-adjusting scales, both with respect to discriminative power and to data adequacy to the assumptions of normality and homoscedasticity. The self-adjusting scale presented a slightly greater discriminative power than the structured hedonic scale, despite the former having presented data with a greater variability and lack of normality of the residuais. Of ali the methods, the ranking test presented the least discriminative power. The structured and hybrid hedonic scales were considered to be signiticantly (psO.01) easier to use than the self-adjusting scale, there being no difference (pSO.O5) between these first two scales. Finally, the objective of the third experiment was to evaluate the performance of the nine-point hedonic, hybrid hedonic and self-adjusting scales in the segmentation of samples and consumers using Internal Preference Mapping methodology. One hundred and twelve consumers evaluated the overall acceptability of 8 commercial brands of red wine, the majority being Cabernet Sauvignon. The effects of presentation order -scales and samples- and carry over effects were balanced. The data were analyzed by ANOVA and MDPREF. Scale performance was evaluated using as criteria: number of significant dimensions in the MDREF (psO.O5), number of consumers significantly adjusted (psO.O5) and the degree of segmentation of the products and consumers. The results suggested a superiority of the hybrid scale over the traditional hedonic and self-adjusting scales. The MDPREF generated by the hybrid scale data produced the greatest number of significant dimensions (p=5%), yielding 79.5% of the consumers significantly adjusted (p=5%), while the MDPREF generated by the self-adjusting scale adjusted 54.5% of the consumers and that of the hedonic scale, 51.8%. Overall, the 9-point hedonic scale showed the worst performance in relation to the other scales examined. The results of this study strongly suggest that the hybrid hedonic scale is a valid and efficient tool for use in data collection associated with consumer studies, both when analyzed by normal models for the analysis of variance and by Internal Preference Mapping methodology (AU) | |