Experienced Yalies know that persistence is the key to successful shopping.

When the student to seat ratio of a lecture creeps above one on the first day of shopping period, they know there is no need to worry. When the syllabi run out, they refuse to panic. When the floor space starts to diminish, they nonchalantly flip through their tattered Blue Books. But when the instructor announces that less than one-fifth of the eager and cramped souls will be allowed into the class, then it is time to leave.

Such was the situation in LC 101 last Tuesday, when instructor Susan Rivers announced that “Social Pyschology” would be capped at 25 students. Less than five minutes into the class, people began streaming out of the doors in disappointment.

“I was frustrated because I really wanted to take the class,” said Cara Demmerle ’06, one of more than 160 students who showed up on the first day of “Social Psychology.”

Demmerle was certainly not the only student frustrated over the last two weeks. This year, as every year, the freedom of shopping accompanied crowded classrooms, limited enrollment, and frazzled professors. “Social Psychology,” “History of Modern China,” and “Biology of Reproduction” are just three examples of this semester’s capped courses.

Yale College lacks a universal policy on course enrollment limitation — a factor that contributes to the mayhem of shopping for classes. Instead, the decision to cap (or not to cap) is left up to individual instructors and their departments.

“It’s very decentralized,” said Barry Kane, the registrar of the Faculty of Arts and Sciences.

This decentralization contributes to a vast range of course sizes. With minimal central regulation of enrollment, the size of Yale classes can range anywhere from one person to the capacity of Yale’s largest classroom, the Law School Auditorium. And, with departments in control, the reasons for limiting enrollment vary from situation to situation.

Last week, over 80 students shopped the first day of “Sport, Society, and Culture,” but only 45 were ultimately admitted. Professor William Kelly and the Anthropology Department decided to cap the size of the class because it has never been offered before.

“I wanted to get a small number of students to help me develop the course,” Kelly said.

But Associate Professor William Segraves’ decision to limit the enrollment size of “Biology of Reproduction” was based on entirely different considerations. Approximately155 students shopped the first day of the class, and around 130 were admitted. Segraves felt that having 155 students would detract from the quality of the class.

“There is something that is lost when a class is that size,” Segraves said.

The wishes of the professor and the department are not the only factors that can determine a course’s enrollment. Occasionally, a lack of available teaching assistants can limit a course’s size. Segraves faced this dilemma in “Biology of Reproduction,” and Jonathan Spence’s popular History of China course was limited for this reason.

“The first two days were pretty wild,” said Spence, who lectured over 500 shoppers last week and ultimately capped the class to 360. Spence described the decision to limit enrollment as “a kind of balance between what I can handle, what the room can hold, and what TAs [are available].”

In addition to class enrollment size, instructors usually determine the criteria for admission to popular classes. Because there is no set policy, numerous systems of priority exit.

In Spence’s “History of Modern China,” priority was given to junior and senior history majors. Open spots were determined through general lottery, in which seniority was not a factor — seniors were just as likely to gain admission as freshman.

“A lot of freshman use this [class] to get involved in Asian and Chinese studies,” Spence said.

Kelly told prospective students in “Sport, Society, and Culture” that the first 45 people who sent in a response to a documentary shown the second day of class would gain admittance. Rivers, a graduate student who limited enrollment in “Social Psychology” because of graduate school requirements, said she simply picked information sheets with her eyes closed.

The unpredictable nature of the enrollment criteria for certain courses may lead to last minute scrambling for replacement classes.

“[Professor Kelly] encouraged people to wait until next year, but there are some of us who won’t be here next year,” said Shoshanna Engel ’03, who shopped “Sport, Society and Culture.” “I had never heard of a professor limiting enrollment in that manner.”

A junior who did not get into Spence’s class shared Engel’s frustration.

“I felt that it might be a good idea to have seniors have priority,” he said. “That way, at least at some point you know you are going to get in.”

Although course listings often sport asterisks and italicized prerequisites, the Yale College Programs of Study frequently does not indicate limited enrollment or typical admittance criteria. The Blue Book’s entries for “History of Modern China” and “Social Psychology” contain no information about size limits.

“I think one of the problems is that [the course information] is put together so early on and so many changes take place,” said Diane Rodrigues, the deputy registrar for Yale College.

“Put it in the Blue Book: Limited enrollment,” Alissa Mohammed ’05 said.

Other schools use different systems of registration that help the process run more smoothly.

At both Stanford University and Brown University, students submit preregistration cards before classes begin, and then are able to add and drop classes during a shopping period similar to Yale’s. This allows professors and administrators to organize classrooms and order materials ahead of time. At Yale, classroom changes often occur after the semester has begun.

“I think it’s mostly a good system,” said Lisa Mandle ’06, a Brown student. “It makes people think about what they want to take ahead of time.”

Susan Maher, Stanford University’s Assistant Registrar, said that while no universal policy for class enrollment exists at Stanford, and professors can “call it how they see it,” enrollment limitations are always included in the published course listings. Late last year, Harvard Dean of the Faculty of Arts and Sciences William Kirby announced that Harvard will begin a system of preregistration next fall as well.

Although Kane said Yale’s Registrar’s office will be paying close attention to the transition at Harvard, he still believes Yale’s current system has merit.

“I think the system we have now is really oriented toward the students,” Kane said.

And despite the problems, most Yalies, like William Chou ’06, defend shopping period.

“It’s frustrating sometimes,” Chou said. “But you have to take the bad with the good and overall I think shopping is pretty helpful.”