The Star Tribune has joined with Piper Jaffray & Co. to create a new Minnesota stock index.

The Piper Jaffray Minnesota index is an equally weighted index of 70 companies, all with market capitalization of more than $100 million as of April 30.

The Piper Jaffray Minnesota index replaces a price-weighted index the Star Tribune used for more than 15 years. Under the new, equally weighted index, all companies contribute the same amount to the overall index.

In the old, price-weighted index, companies with higher stock prices had more impact than those with lower stock prices. So Buffalo Wild Wings, whose shares trade at more than $150 per share, had more impact on the index than General Mills, whose stock trades in the $55 range but has more than 10 times the annual revenue of Buffalo Wild Wings.

The new index is meant to show the collective health of Minnesota’s public companies and to offer a comparison to the overall market. It includes companies with a corporate headquarters in Minnesota but officially domiciled elsewhere, like Medtronic and Pentair. It also includes companies that have a strong Minnesota presence and more than 3,500 employees in the state. Wells Fargo, Delta Air Lines, Thomson Reuters and Honeywell are included for this reason.

“Minnesota companies continue to outperform the average stock,” said Craig Johnson, a senior technical research analyst for Piper Jaffray, who built the new index.

Johnson supplied 20 years of pricing history. He started the index with the base year of 1995 and a base value of the index of 100. The index closed May 1 at 680.42.

The new Piper Jaffray Minnesota index will be used only for information purposes.

Johnson is in charge of Piper’s proprietary technical research group, which specializes in creating custom sector and industry group data. For example, the group has a 3-D printing company and an oil field services index.

Over the years, Piper has made significant investments in collecting pricing and fundamental data on thousands of companies. Johnson has data on about 5,000 companies with a market capitalization greater than $25 million and a share price of more than $2.

“We own the data and can proactively check and keep the data clean,” he said.

Johnson, who along with his group was recognized last month for his technical research and strategy at an industry awards program, also invested heavily in automating the collection of the data, giving his team the speed and flexibility to analyze the information and provide custom reports.

The index represents several different industries and includes companies of many different sizes, from the $130 billion health care giant UnitedHealth to Brooklyn Park-based Mocon, which makes packaging and materials testing instrumentation and has annual revenue of $64.5 million.

The Star Tribune will publish the index’s close and weekly and yearly change each Monday.