MIRROR, MIRROR; The Anthropologist Of Dressing Rooms By Penelope Green Published: May 02, 1999 Sign In to E-Mail Print Single-Page IN a dressing room deep in the men's department of Macy's in Paramus, N.J., a lone linty french fry nuzzled a balled-up Kleenex. A few cardboard strips, discarded from shirt collars, beckoned from across the maroon carpet. Straight pins glinted shyly under a bench. Paco Underhill, retail anthropologist and passionate shoppers' advocate, gave me a withering look. Macy's, the look said, wasn't doing its job, and he was mad about it. ''Righteous anger,'' Mr. Underhill had explained earlier, ''is very much a part of my personal universe.'' He stomped out of the dressing room -- at 6-foot-4, Mr. Underhill is good at making a point with his body. Nobody feels a shopper's pain more acutely than Mr. Underhill, the 47-year-old founder of Envirosell, a market research company that studies shopping habits, and a disciple of the late urban anthropologist William H. Whyte. As Whyte did, Mr. Underhill applies the field-study methods of a behavioral scientist. Envirosell researchers, known as trackers, follow shoppers around stores, recording their every twist and sidle, their every pat and fondle of the merchandise. Their notes are supplemented by miles of what Mr. Underhill calls ''the most boring'' videotape, to understand how people navigate stores, and what attracts or repels them. In a new book, ''Why We Buy: The Science of Shopping'' (Simon & Schuster), Mr. Underhill reveals that Americans walk the way they drive -- on the right -- and so they habitually veer to the right aisles of a store. (Australians and the British, by contrast, veer to the left.) Mr. Underhill knows that most people, especially women, don't like to be jostled or nudged on their bottoms when they are shopping, and they will walk away even if they might have been interested in buying. (When Mr. Underhill first observed this ''butt-brush factor'' at Bloomingdale's and described it to the store's president, a tie rack was moved out of a narrow traffic lane, and, in the following weeks, Mr. Underhill said, sales of ties soared.) Mr. Underhill knows that 65 percent of men who take jeans into a dressing room to try them on will buy them, and that only 25 percent of women will. And he knows that a woman shopping with a man will spend less time in a store than if shopping alone, or with a friend, or even a child.