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Repertory Grid Technique (RGT)

If you were using the Repertory Grid Technique (or RGT), you begin with the knowledge elicitation phase where you try and see into how your subject perceives the stimuli. You present three cups of coffee (say, A, B, and C) to the subject and ask ``Pick the two cups of coffee that are most similar and tell me what makes the other one different.'' You now have two attributes - for example, the subject might say something like ``These two are bitter whereas the third is sweet.'' So you write down the word ``bitter'' under the heading ``Similarities'' and ``Sweet'' under the heading ``Contrasts'' as is shown in Table 5.3

Table 5.3: An example of some similarities and contrasts in four different coffees. These classifications are found in the knowledge elicitation phase of the RGT.

Similarity	Coffee A	Coffee B	Coffee C	Coffee D	Contrast
Pole					Pole
Bitter					Sweet
Cold					Hot
Light					Dark
Strong					Weak
Etc.					Etc.

Repeat this process with three different cups of coffee, randomly selected from the four different types. Keep doing this until the subject stops giving you new words.

Now you have a ``rating grid'' (shown in Figure 5.3, ready to be filled in by the subject). So, you ask the subject to taste each of the four cups of coffee and rate them on each attribute scale using a number from 1 to 5 where 1 indicates the word in the Similarity Pole and 5 indicates the word in the Contrast Pole. For example, the subject might taste Coffee A and think it's very sweet, so Coffee A gets a rating of 5 on the Bitter-Sweet line. If the same person thinks that Coffee B is neither too bitter nor too sweet, ti might get a 3 on the Bitter-Sweet line.

An example of the ratings to come out of this rating grid phase is shown in Table 5.4.

Table 5.4: An example of the ratings of four different coffees. These ratings are found in the rating grid phase of the RGT.

Similarity	Coffee A	Coffee B	Coffee C	Coffee D	Contrast
Pole					Pole
Bitter	5	3	2	1	Sweet
Cold	4	4	5	4	Hot
Light	2	4	3	5	Dark
Strong	1	3	2	4	Weak
Etc.					Etc.

The nice advantage of this technique is that each individual subject rates the stimuli using attributes that they understand because they came up with those attributes. The problem might be that they came up with these attributes because they thought you wanted to hear those words, not because they actually think they're good descriptors. Also, there is the problem that every person in your panel will come up with a different set of words (some of which may be the same and mean different things, or may be different and mean the same thing...) This can be a bit confusing and will make your life a little difficult, but there are some statistical software packages out there that can tell you that two people mean the same thing with different words (because their ratings will be similar) or that they're using the same words to mean different things (because their ratings will be different...)

In order to analyze the results of an RGT rating grid phase, people use various methods such as factor analysis, principal component analysis, multidimensional scaling and cluster analysis. I will not attempt to explain any of these because I don't know anything about them.