To evaluate prices, we conducted a market-basket price survey. The market basket consisted of 151 items and included national-brand non-perishables and fresh produce, meat, and dairy products. Our price comparisons table shows how each store’s prices compared to the average prices for national-brand and non-brand (fresh meat, produce, and dairy) items at all surveyed stores. The survey was conducted from July 12 to 22, 2015.

The “Overall prices” tab of the price comparisons table shows how each store’s national brand non-perishables and fresh produce, meat, and dairy products stacked up. The $87 score for the Walmart Neighborhood Market in Chicago shows that it was about 13 percent cheaper than the average prices at all surveyed stores for the same products. The $106 score for the Jewel-Osco in Lockport means that its prices were about six percent higher than the all-store average. (Since the market basket includes fresh meat and produce, store-to-store quality differences may account for some price differences. Also, savings might vary depending on such factors as the extent to which shoppers take advantage of specials and coupons.)

For our survey, we used available sale prices and we assumed shoppers would use club cards at all stores that offered them.

The “Cheapest brands” tab of the price comparisons table shows the effect of substituting the cheapest available brand in each store for 26 national-brand items. The Mariano’s in Oak Lawn, with a score of $90, beat SuperTarget’s prices by about six percent when we substituted the cheapest brands in place of some national brands at each store.

The “Variety” tab of the price comparisons table also shows the percent of market-basket items that our shoppers found at each store. For example, the Mariano’s in Arlington Heights carried 91 percent of the items in our full market basket that contains national brands.

To compare Trader Joe’s and Aldi’s prices with prices at conventional supermarkets, we used the modified survey described in the text of this article. Our section on comparing Trader Joe's and Aldi's prices describes this survey and shows the results of these comparisons.

We also used a modified survey to compare prices between conventional supermarkets and warehouse stores. Our section on warehouse stores reports those findings.

In our tab comparing stores’ Service quality, we report ratings we received from area consumers (primarily CHECKBOOK and Consumer Reports subscribers) of stores’ products and service. The survey asked respondents to rate supermarkets “inferior,” “adequate,” or “superior” on various aspects of quality, from “quality of fresh produce” to “convenience of store layout” to “overall quality.” Our ratings tables reports (for chains that received at least 10 ratings) the percentage of customers who rated it “superior” on each question.