It's no secret that long wait times are a simmering shopper frustration, but how long is too long? At grocery stores, more than four minutes can jeopardize a customer’s loyalty, said a research firm that released new shopper data last week.

A study conducted in early 2007 by M/A/R/C Research found that 10 percent of shoppers were exasperated enough to leave a checkout line if the wait was lengthy, and the marketing research firm decided to run an online survey of almost 13,000 consumers this year to discover the importance checkout times had on their most recent shopping trips, and whether attitudes had changed since the earlier study. The results were consistent with last year's findings, said the research firm.

As in 2007, the new study showed that shoppers' satisfaction remains high when in line four minutes or less in all store categories. The only exception is for club stores, where an average wait time slightly over four minutes was deemed still acceptable by those surveyed. After four minutes, the satisfaction levels drop considerably across the other seven categories: grocery, consumer electronics, department, drug, home improvement, mass merchandisers, and office supply stores.

One result Dallas-based M/A/R/C found surprising was that 43 percent of consumers said long lines would affect their decision to shop a particular retailer in the future -- and out of those consumers, 3 percent said they'd stop visiting the store altogether.

"Retailers really have to focus on keeping their wait times under four minutes, with the negative impact of even one minute more," said Tony Amador M/A/R/C’s s.v.p.

The study offered a list of leaders in conversion (shoppers that purchase) and lowest wait time in each category, in addition to a look at which days of the week reported the shortest lines, and the satisfaction levels with wait times by age group. Publix was the leader among grocers.

To download the full study, go to http://www.MARCresearch.com/measure.