Backstory: Mrs. Murphy, inflation detective

It's 9:25 a.m., the kids are safely dropped off with relatives, and Beth Murphy is ready to embark on another binge of serial store-hopping. Before she picks her son and daughter up again in the early afternoon, she'll visit a clothing store, two supermarkets, a pharmacy, a sporting goods outlet, and a camper-trailer sales lot.

But Mrs. Murphy is no shopaholic. She's a mild-mannered price detective who buys nothing. She reveals data only to bureaucrats at the US Department of Labor. And the products she checks are the same ones she priced last month, and the month before, and the month before ....

The result is one of the most closely watched indicators of the economy's health – the consumer price index, or CPI. Everything from the direction of interest rates to the annual adjustment of Social Security benefits is pegged to it. July's CPI is set for release Wednesday morning at 8:30 and will help the Federal Reserve decide whether to raise short-term interest rates in a battle against inflation.

The CPI couldn't happen without the work of Murphy and about 400 other part-time "economic assistants" who gather data across the nation.

Their skills are developed on the job – starting with two weeks of intensive training in Washington. But the Labor Department looks for people with proven aptitudes and affinities such as math, marketing, or statistics. Murphy has a degree in economics. The pay is often $14 to $22 an hour for an average of 22 hours a week.

On her shopping foray last week, Murphy was dressedmuch like anyone on a humdrum shopping trip – but with a professional focus.

9:30 a.m. She pulls into a parking lot in Tyngsboro, Mass., just south of the New Hampshire border, to check the biggest item on her shopping list from a category that her bosses call "unpowered boats and trailers." But on stop No. 1, Murphy hits snag No. 1. Her target – a specific brand of camper-trailerwith a fold-down tent – isn't in stock. Two were sold recently, a manager says, and there are no more on the lot. She can't just ask what the price will be when the camper is restocked. The Labor Department's Bureau of Labor Statistics requires Murphy to get today's price, not yesterday's or tomorrow's. (And she's not supposed to reveal names of stores she visits or specific products she looks at.)

9:50 a.m. Now, Murphy pulls into a sporting goods store in Hudson, N.H., and golf is on her mind. She doesn't play, but in 15 years collecting data she's learned many things, including the technology behind the golf club she's checking.

"It's just called a wood. They're not made of wood anymore," she says. Faced with a sea of competing brands, she finds the club she's looking for.

She frequents this store, like all the others, because a data analyst in Washington sent her there. The Labor Department decides these things based on a Census Bureau survey of what real-life Americans say they buy and where. Once in a store, however, it's up to Murphy – drawing on disciplined training – to define the specific products she'll check each month. Essentially, the system is designed to ensure that, if she's just going to check two or three items each month, those items are representative of what that store is selling.

On her first visit to retail outlets, Murphy talks to managers about what they sell. She enters broad categories into her hand-held touchscreen computer, which then makes random choices for her. "You're grouping and you're randomly narrowing down," to a single product to check, she explains.

That's how she got her golf list: A single 9-wood club, a full set of irons, a box of balls, and a pull-cart for clubs. She samples these items six times a year. Today, they're all in stock – a price-checking grand slam.

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