– Ancestry-testing firm 23andMe’s spit tests for insights into family history and health are top sellers on Amazon, but its ancestry test and those from three other companies produced drastically different results, a new report found.

“23andMe’s ancestry results were the most confounding of all,” said Kristen Brown, writing in Gizmodo about her efforts to uncover the secrets of her ancestry via tests from 23andMe, Ancestry.com, National Geographic and Gencove. “It found that I was only 3 percent Scandinavian, a number that, based on my recent family history, I know is flatly wrong.”

In interviews this week, three of the four companies defended the value of their services but admitted limitations in accuracy of results.

Critics who closely watch the industry, however, said that the companies are misleading consumers.

Brown received test results that varied widely as to how Scandinavian she was, and although testing firm Gencove reported that 8 percent of her DNA was from the Indian subcontinent, 23andMe said she had no South Asian DNA.

“Four tests, four very different answers about where my DNA comes from — including some results that contradicted family history I felt confident was fact,” Brown wrote in the article.

Company representatives made it clear that the popular DNA ancestry tests — ranging in price from $60 to $100 — produce estimates, rather than certain results.

A Gencove spokesman said the company, which has DNA information on “tens of thousands” of people from public databases and its own customers, had “only a limited view of the genetic diversity across the entire world.”

When a new customer has ancestry unlike anyone profiled before, algorithms that assign ancestry make a “best guess,” which is “usually close but imperfect,” said Gencove spokesman Joseph Pickrell.

In an e-mail, 23andMe spokesman Andy Kill said the company was “very confident” in the results reported to customers. The conclusions on ancestry depend on the degree of confidence the company has that a person’s DNA points to a particular country or region, Kill said.

DNA tests for ancestry are more toys than scientific tools, said Charles Seife, a journalism professor at New York University who monitors the business. “A lot of this stuff is really for entertainment only.”