To evaluate prices, we conducted a market basket price survey. The market basket consisted of 154 items and included national-brand nonperishables and fresh produce, meat, and dairy products. Our ratings tables indicate how each store’s prices compared to the average prices for national-brand and non-brand (fresh meat, produce, and dairy) items at all the stores we surveyed.

Our ratings tables report price comparison scores, which indicate how the chains and stores stack up when compared to the average prices offered by all surveyed stores. A score of $90 indicates prices about 10 percent cheaper than the all-store average for the same products; a score of $110 indicates prices about 10 percent more expensive than average.

Clicking on the name of a chain or store pulls up a detailed ratings page for it. These report a separate price comparison score for only the fresh produce items in our market basket, a score for the fresh meat items, and a score that indicates the effect of substituting the cheapest available brand in each store for about one-sixth of the national-brand items.

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 assumed shoppers would use club cards at all stores that offered them.

To compare prices at specialty stores, such as Trader Joe’s, with prices at conventional supermarkets, we used a modified survey that compared the prices of their independent store brands against the national-brand products in our market basket. (When comparing prices, we used per-unit pricing—for example, price per ounce.) We also used a modified survey to compare prices between conventional supermarkets and warehouse stores.

We also did a separate comparison for warehouse stores. Because these outlets stocked so few items in the sizes of our basic market basket, we looked for items of any size, so long as they were the same brands. We then used unit prices (for example, price per pound) to calculate the warehouse stores’ prices for amounts specified in the market basket. After this adjustment, we compared the prices of items at the warehouse stores with prices for the same brands at several other stores. Bear in mind that this is not an “apples-to-apples” comparison; the sizes of the items priced at the warehouse stores were usually larger than the sizes of the items priced at the other stores, so the warehouse stores enjoy an advantage in such a comparison.

We also used our market basket survey to shop prices at grocery delivery services. We then compared the cost of groceries at these services with the average costs we found at local grocery stores, assuming you’d spend $200 a week at the average-cost local supermarket and get one delivery a week and taking into account any additional delivery fees and a 10 percent tip (for companies that allow gratuities).

All our price research was conducted May 11–21, 2018. Keep in mind that grocery store and delivery options are changing rapidly—a few went online or disappeared while we were doing our price research and writing this. Notably, Walmart continues to expand its delivery service areas around the U.S., and Amazon continues to tinker with its new Whole Foods acquisition. By the time you read this, more changes likely occurred.

Our ratings tables also report how area consumers (Checkbook subscribers plus other consumers we randomly invite to take our survey) rated 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 report (for chains and stores that received at least 10 ratings) the percentage of customers who rated it “superior” on each question.