[ARSCLIST] ABX for Dummies

[Bruce Kinch <bckinch@xxxxxxxxxxx>]

I joined this list only recently, and was rather nonplussed that some 
early comments resulted in challenges to submit my personal 
observations to ABX testing. I demurred with as much good humor as I 
could muster, even after a suggestion that I was “afraid” to do so. 
Several references to Boston Audio Society papers were made, and I have 
noticed that other posters have gotten responses that reference the 
same test protocol, and that more posts have recently commented on it. 
While this list is far more civil than a Rec Audio newsgroup back when, 
it was evident that proposing an ABX test remains a convenient 
rhetorical device to dismiss an opinion with which one disagrees.

My undergraduate degree was in (Experimental) Psychology, so I have 
some conceptual understanding of and respect for the problems of test 
design. I was also a dues-paying member of the BAS back in the day (so 
was CJ, I think), so I am familiar with their fascination with ABX 
testing. My most recent encounter with such a test was at The Home 
Entertainment (parasite) Show at CES in Las Vegas last month. The tests 
were run by, believe it or not, the Wall Street Journal. The sound from 
either A/B choice was so a-musical I walked out, chuckling in 
amusement. But it was probably not the worst sound on hand in Vegas 
that week, either.

First, let me suggest that anyone who demands an ABX test as “proof” of 
another’s personal experience, but who has never actually designed or 
even participated in one is simply blowing smoke, and should refrain 
from doing so here.

Second, for anyone on the lists unfamiliar with ABX tests but given to 
intellectual curiosity, I can suggest a simple, free illustration of 
the process. ABX testing involves exposing a subject to sample A, then 
sample B. Sample X is then provided, and the subject decides whether it 
is identical to either A or B. If it is a double blind test, neither 
the subject nor the tester knows what A, B, or any X is. If you Google 
ABX, you will find a lot of angry audiophile bickering, but an ABX test 
can be designed for any situation that involves the cognitive processes 
of perception, memory, and identification. So, with apologies for the 
added bandwidth, a challenge follows:

Go to a paint store. As we want to avoid “coloration”, go to the rack 
of “Neutral” paint patch strips, and choose one where the differences 
in tint, hue, and saturation are minimal. (Of course, to be truly 
”blind”, you can have someone else do all this). While the clerk is 
distracted, swipe 11 strips. After you get past mall security, pick the 
two patches that are the closest. Let’s say they are called Pewter Fog 
and Pearl Mist. Cut out the patches (eliminating the names) and label 
the backs of Pewter Fog A and the Pearl Mists B. Cover 10 sets of A and 
B labels with opaque but removable tape. Set aside the remaining pair 
labeled A and B, and dump the rest into a bowl deep enough that the 
contents cannot be seen or counted.

Place the two labeled A/B patches in front of the subject, label side 
up. Place one empty deep bowl labeled A to the left, and another 
labeled B to the right. Put the bowl of taped samples where they can be 
reached but not seen.

The subject (it can be yourself) can turn over A and examine it but 
must replace it face down to look at B, and vice-versa. Placing both 
face down, a sample is drawn from the bowl, and the subject must decide 
if it is identical to A or B, and place it in the appropriate bowl. The 
process is continued until all the samples are sorted. You can then 
peel back the tape and see how many were correctly ID’ed and sorted. 
Any more than 10 correct and you are better than chance. Score 20 and 
you can be referred to on this list as “Golden-Eyed”.

While this seems a pleasant enough parlor game, it would not cut the 
mustard in even an intro course in Experimental Psych. The result above 
is just a single data point; one needs another variable for the test to 
have meaning. Repeat the test several times to see if the skill can be 
learned. Test 100 people and sort by age, gender, religion, etc. Change 
the lighting from incandescent to fluorescent. Compare putative experts 
(artists, house painters) to the overall population. Choose different 
patches and correlate to the pigment differences. Etc. And of course, 
you can have lots of fun twisting the statistics, but we won’t go there 
right now.

If very few subjects can reliably tell the difference between Pearl 
Mist and Pewter Fog, they are perceptually identical, according to the 
statistics typically applied. If the new CEO of Benjamin Moore was 
hired from Crayola, he may decide to "dumb down" the variety of colors 
available and eliminate one (or both) colors from the line in order to 
impress the stockholders with his bold vision. Of course, the test 
actually tells us nothing about the qualities of paint that determine 
consumer preference – like durability, fade resistance, hiding power, 
etc. Or which shade your mother would choose for the dining room. And 
the marketing dept would never let such decisions be made “blind”, 
anyway. The use of evocative names acknowledges that some buyers would 
prefer a rich, luminous shade like Pearl Mist rather than a cool 
metallic one like Pewter Fog, even if the two shades can’t be 
distinguished by ABX testing. And of course, the putative “Golden-Eyes” 
like artists or housepainters would do no better than average folk 
because their background involves no special training in remembering 
subtleties of dried paint chips, even if they splash around in wet 
paint every day.

I realize of course, that resorting to “analogies” might rile up some 
of the more “scientific” types on the list, but perhaps actually 
participating in a simple double blind test can illuminate some of the 
grey (or is it gray?) areas in such discussions.

More to come.

Bruce