Quantitative Descriptive Analysis

Quantitative Descriptive Analysis (QDA®)

 
Quantitative Descriptive Analysis (QDA®) is one of main descriptive analysis techniques in sensory evaluation. QDA® was proposed and developed by Tragon Corporation under partial collaboration with the Department of Food Science at the University of California, Davis. Initial intentions for this method were to deal with poor statistical treatment on data obtained by Flavor Profile and related descriptive methods2.
 
In the QDA® methodology, multiple product evaluations are suggested to capitalize on panelists’ skill in making relative judgments with a high degree of precision. Humans are good at judging relative sensory differences but poor at evaluating absolute differences3.This philosophy has made QDA® methodology distinctly different from those descriptive methods which try to finalize the absolute difference among products (e.g., Spectrum method).
 
Similarly to other descriptive methods, subjects are screened based on their performance on discrimination tests and verbalization in the QDA® methodology. Standards for subject qualification are arbitrary and may vary depending on the project. A panel of ten to twelve is recommended in QDA® 3. During training, test products are served as illustrative stimuli for the consensus language development. The panel leader works as a communication facilitator without involvement and interference with panel discussions. References can be used for generating sensory terminologies, especially when panelists are confused and disagree with each other on some sensory attributes during training sessions3.
 
Line scales are employed for panel training and data collection in QDA®. This line scale is designed as 6-inch in length with sensory intensities word anchors located 0.5 inch from each end. The scale direction goes from left to right with increasing intensities, e.g., weak to strong, little to much3.During data collection, panelists measure sensory intensities independently at individual booth without reference served as intensities standards. Panelists are allowed to use different parts of the scale to determine the sensory intensities by themselves. As a result, the difference among products produced by QDA® will be a relative measurement; the importance of absolute scale value has been neglected1. Subjects’ reliability is evaluated by their repeated measurements on product attributes.
 
The results from QDA® are informative for statistical practices to meet project goal. Panel performance can be examined by interaction of product and panelist; product difference can be diagnosed by means of a one-way AOV based on attributes. Statistical procedures, such as multivariate analysis of variance, principle component analysis, factor analysis, cluster analysis can be widely applied to QDA® dataset1;means of attributes in the same sensory category can be graphically presented by a “spider web” , see figure 1.
 
QDASpiderWeb.jpg

 
Figure 1. Graphical display of sensory attributes based on QDA® result3.

References

 
1 Lawless HT., Heymann H. 1998. Sensory Evaluation of Food: principles and practices. New York, NY. Chapman &Hall; Press.
 
2 Meilgaard M., Civille GV., Carr BT. 2007. Sensory Evaluation Techniques. 4th ed. Boca Raton, FL. CRC Press.
 
3 Stone H., Sidel JL. 2004. Sensory Evaluation Practices. 3rd ed. San Diego, CA. Elsevier Academic Press.