Overview of Descriptive Analysis

The aim of all descriptive techniques is to generate quantitative data which describes the differences among a set of products. Each method has a slightly different approach to solving the same problem; however the basic framework of all the techniques is the same:

• selection of panel members
• term generation (or selection of appropriate lexicon)
• concept formation
• testing of panel consonance
• evaluation of products

Descriptive techniques include Free Choice Profiling (FCP), the Spectrum™ method, Quantitative Descriptive Analysis™ (QDA), Flavor Profile Method, Texture Profile Method, Flash Profiling and generic descriptive analysis. Generic descriptive analysis generally takes pieces from QDA and Spectrum™ methods, but is tweaked to suit the goals of the project and limitations of the product being tested. Of the methods mentioned here, FCP and Flash Profiling involved the use of untrained consumers rather than a trained panel (although a trained panel can be used). This main point of differentiation makes these techniques faster and cheaper to conduct as there is no training involved.¹²

Panel Selection

The selection of panel members is very important to the quality of the data obtained. Potential members need to be screened for their ability to discriminate between similar samples, rate products for intensity and identify tastes and aromas. Equally, or possibly more, important than a panelists’ sensory acuity is their motivation. A panelist who feels they are required to particiapte may not perform as well as and equally skilled panelist who feels motivated to participate.

Panel Training

Panel training encompasses term generation, concept alignment and panel testing phases. The amount of training required is dependent upon the method used as well as the product(s) to be tested.³ A company with an in-house descriptive panel may spend several months or more training a panel over a wide range of products, rather than training the panel specifically for each product as needed.

Notes

¹ Lawless, H. and H. Heymann (1998). Sensory Evaluation of Food: Principles and Practices. New York, Kluwer Academic/Plenum Publishers.

² Murray, J. M., C. M. Delahunty and I. A. Baxter (2001). Descriptive Sensory Analysis: Past, Present and Future. Food Research International, 34: 461-471.

³ Chambers, D. H., A.-M. A. Allison and E. I. Chambers (2004). Training Effects on Performance of Descriptive Panelists. Journal of Sensory Studies, 19: 486-499.

Multiple Factor Analysis

Multiple Factor Analysis (MFA) is a statistical technique based on PCA used to analyze multiple sets of data pertaining to the same set of products. Although all the variables could be combined into one large data set and analyzed by PCA, one group of products may exert more influence on the construction of the product space than other sets of variables. MFA solves this problem by giving equal weighting to each defined group of variables.

During the first step of MFA, a PCA is performed on each group of variables. Then the groups are normalized by dividing all the variables within a group by the first eigen value for that group. All the variables are then combined into a single data set and a global PCA is run.

Applications

There are many uses to which MFA is well suited. It can be applied to a variety of data sources, provided that all the variables within each group are either quantitative or qualitative (not both). However MFA can be used to combine a group of quantitative variable with a group of qualitative variables. Applications of MFA include:

• analysis of projective maps
• comparison of panels describing the same products
• combination of descriptive and chemical data
• comparison of product spaces obtained by different descriptive techniques

Perceptual Mapping

The term perceptual mapping refers to a collection of techniques which can be used to generate graphical representations of perceived product relationships. Although they generally also contain relevant product attributes, lending interpretability to the map, it is not necessarily a requirement. It is an invaluable tool to reduce a large data set with numerous attributes into an easily interpreted 2-dimensional plot. One hazard is some loss of data inherent in this type of analysis. A 2-dimensional plot may not fully, or accurately, depict the relationships among products or between products and attributes.

The type of data available has an impact on the statistical procedure used to generate the map. Data such as that obtained from descriptive analysis can be readily analyzed by Principal Component Analysis or PCA. However data obtained from a sorting task cannot be evaluated in this manner, but can instead be analyzed by Multi-dimensional Scaling (MDS) or a similar technique. Other methods to generate perceptual maps include Multi-Factor Analysis (MFA), Generalized Procrustes Analysis (GPA) and Discriminant Analysis.

Applications

Perceptual mapping is a popular tool in market research. In this context it can be used in product category review. Maps can be generated which depict where currently available products fall in relation to each other and what attributes consumers associate with these products. When combined with consumer preference data it may be useful in determining opportunities for product placement.

Although members of The Society of Sensory Professionals (who are logged into their society account) can edit or create wiki articles, non-members are welcome to submit material through the wiki editorial board.

The society welcomes and appreciates all contributions, but we ask that you do not contribute any copyrighted material.

If you are new to this wiki, you may want to read the help page and become familiar with the general structure and some special formatting rules, including article style.

If you’re not sure what a wiki even is, you might want to take a look at an article on wikis by one of the more famous wikis on the Internet.

Principal Component Analysis

Principal component analysis (PCA) is a type of factor analysis which can be used to generate a simplified view of a multi-dimensional data set, such as those from descriptive analysis. The data set is reduced to a smaller set of underlying factors based on the correlations of the original variables. PCA uses linear transformation to generate a set of uncorrelated principal components (PCs). Each principal component is a linear combination of the original variables. The largest amount of variation in the data set is aligned with the first PC, the next greatest amount of variation is assigned to the second PC, and so on¹ .

Because PCA involves a linear transformation, it merely involves a change in the viewpoint of the data, as opposed to creating something new. PCA generates factor loadings, representing the correlation of attributes to the new dimensions (PCs), and factor scores which represent the values of the samples in the new space.

PCA is commonly used to provide a way to visualize the relationships among products and attributes. It can also be applied to a set of consumer liking data to generate an internal preference map.

Notes

¹ Lawless, H. and H. Heymann (1998). Sensory Evaluation of Food: Principles and Practices. New York, Kluwer Academic/Plenum Publishers.

Editing Wiki Articles

In addition to the general help information and article style help, there are a couple of things you should know when editing existing wiki articles.

When you are in edit mode, there will be a large text box that contains the article itself, and underneath the text area will be three additional fields:

• Notes
• Redirect
• Rename

Notes

The notes field should alway be used to provide a brief statement of what sort of editing is being done. Currently, the field only supports a maximum of 80 characters, so you cannot be verbose; however, including some indication of why a change is needed will helpful to reviewers.

Redirect

The redirect field should only be used when you want a search or page reference to go to an existing article. For example, suppose that there is already an article on context effects that covers carryover. In this case, you might create an article called “carryover” and specify, in the redirect field, “context effects.” Then, any search or reference to carryover would send the read of the wiki to the main, context effect piece.

Rename

The rename field is used to change the current name of the wiki article. This could be a simple as needing to fix a typo, or a more involved situation where a topic is split into multiple pieces, and the existing article needs to be renamed.

Style of wiki articles

When creating a new wiki article, please following the style guidelines described below. Having a consistent style is very important for readability.

Article Page Name

First and foremost, please choose an article page name fairly carefully, as this will be the system identifier of the article. The page name should be as short as possible without unduly sacrificing specificity. For example, an article on palate cleansing could be named “palate cleansing” if it was a general treatment of the topic, but if it was specific to spicy foods and there was already an article that dealt with, say, lingering sweeteners, you may then want to include “spicy” in the page name.

Also note that when a wiki article refers to another wiki article, it will do so using the page name as the text of the (internal) hyperlink. Hence, an article page name should be something that can be logically and readily used in a sentence.

Assigning a Category

To help organize the wiki, articles are assigned to categories. For example, this article was put under the “help” category. There are also several articles that are under “basic taste.” If the article can be placed within an existing category, it should be. But it may certainly happen that a new category is the first of its kind.

There is a special syntax used to assign an article to a category. The word “Category” and the name of the category must be separated by a colon and enclosed with a set of matching double brackets. So, for example, this article was categorized by using the following as the first line:

Formatting

Please set the name of the article, which can be longer than the article page name, in larger text using a heading style of “h1”. To do this, simply type “h1” followed by a period, and then a single space before the title text.

Internal references (hyperlinks)

Material already in the wiki should never be copied and pasted into another article, but, instead, it should simply be referenced. To reference another page within the wiki simply enclose the article name within matching double brackets. For example, suppose we wanted to refer back the general, main, help page. In the article, such a reference would look like this: help. When editing, this reference would be entered as follows:

External references (hyperlinks)

When an article needs to reference a web page external to the wiki — that is, to provide a standard hyperlink — the syntax for that is somewhat more involved. Suppose that you wanted to reference wikipedia’s article on wiki’s and have the hyperlink formatted as: what is a wiki?. This would be accomplished as follows:

"what is a wiki?":http://en.wikipedia.org/wiki/Wiki

Notice that the hyperlink text is first and enclosed in double quotes, followed by a colon, and then finally the full URL.

Footnotes

Whenever possible, if statements are made that are not common knowledge, or a quote is used, a reference needs to be given. In order to avoid hard-to-read, cluttered text, references can be included through the use of footnotes. A footnote can be included by just enclosing its sequential number in matching single brackets. Later, at the end of the article, the footnote text is specified with the “fn” command followed by a number, immediately next to the text.

For example, suppose one made the following quote:

You can, for example, never foretell what any one man will do, but you can say with precision what an average number will be up to¹.

The footnote reference was entered as follows:

... average number will be up to[1].

Later, the actually footnote might look like:

¹ Sherlock Holmes in “The Sign of Four,” 1890.

And was entered as follows:

fn1. Sherlock Holmes in “The Sign of Four,” 1890.

Article Discussions

Because the society site has forums built-in, any discussions of article content should be done using the
article forum. Also, if there a discussion thread for an article, there needs to be a hyperlink in the article to the discussion thread. The link should be given at the bottom of the article, and should be titled “Article Discussion.” As an example, the link to the discussion thread on help articles would look as follows:

"Article Discussion":http://www.sensorysociety.org/ssp/forums/viewthread/4/

The number associated with a specific thread can be obtained by inspecting the link to the thread in the forum itself.

Umami and MSG

The view of MSG as a flavor enhancer is incorrect. MSG (and certain other amino acids) give rise to a 5th distinct gustatory quality that is commonly called umami. Unfortunately, much like the dreaded Tongue Map, many texts still persist in denying umami as a 5th taste quality and instead refer to MSG as a flavor enhancer. The functional expression of a human taste receptor for glutamate should hopefully win over the remaining skepics.¹

See also:

• Bruce P. Halpern. 2002. What’s in a Name? Are MSG and Umami the Same? Chem. Senses 2002 27: 845-846.

• Bernd Lindemann, Yoko Ogiwara, and Yuzo Ninomiya. 2002. The Discovery of Umami. Chem. Senses 27: 843-844.

Notes

¹ Edited from a Sensory Nexus posting by John E Hayes, Sept 18, 2003.

Try Editing this page

If you’d like to get some experience in editing a wiki page, please click on the “Edit” tab above this article. But please don’t delete any of the various syntax examples; that is, please leave it in a form that will be helpful to the next person.

When you’re in edit mode, you should (if someone didn’t delete it!) see that the category of the article is declared in the first line. Note that the category an article is assigned to follows immediately after the colon.

If you want to add various highlighting to your text, you can do:

• Use a pair of asterisks to make bold text
• Use a pair of underscores to make italic text

Using a single asterisk (followed by a space) at the start of a line will make a bullet list (as seen above).

In order to refer to another page within this wiki just enclose the name of the page in double brackets. For example, to refer to this page within a different wiki article, you’d simply use double left brackets, the text “try me”, and then a closing double right brackets. The result would look like this: try me.

To link to an external web page, the syntax is a bit more complicated. First, enclose the text portion of the hyperlink in double quotes, followed immediately by a colon, :, and then end with the full (http) URL. So, for example, the home page of the society might be shown as: Society of Sensory Professionals.

The major sub-sections of an article should use an h2 header style.

And sub-sub-sections can use an h3 header style (and so on).

General Help

Please note that in order to create a new page or edit an existing wiki article, you must be a logged-in member of the society.

Before creating a new article, it is a good practice to make sure that one doesn’t already exist by using the search function (left-hand side column). If you know that the article doesn’t exist, then you may want to use the “create or find page” field (also on the left). If the page exists, you will be taken to it; otherwise, you will be taken to a blank page where you can then click on the “edit” tab to compose the article. Please note, though, that entering a page name will turn up an article only if the article’s page name is an exact match. The search, on the other hand, will do a general search.

Formatting in wiki articles

This wiki uses special syntax in order to handle various types of content. There is syntax associated with instructing the wiki about what category the article belongs to, and syntax for text formatting. The so-called markup language used for text formating is called “textile”¹.

You can learn more about Textile at the author’s web site, which allows you to experiment with the various text formatting strings, or you could also look at or play with the try me page.

Before creating your first article, please read the information on this wiki’s article style conventions. Also, article editing contains some information on special fields used when revising an existing piece.

Notes

¹ http://en.wikipedia.org/wiki/Textile_(markup_language)

Article Discussion