The share of English speakers in Quebec has decreased — not increased — since 2011, according to figures released by Statistics Canada on Thursday after an error in how the 2016 census responses were counted was discovered.

The new numbers show the share of Quebecers with English as their only mother tongue decreased to 7.5 per cent from 7.7 per cent in 2011, rather than the increase to 8.1 per cent that was first indicated when the language results from the 2016 census were released earlier this month.

A shrinking share of Quebecers say English is the language they speak most often at home, decreasing to 9.7 per cent from 9.8 per cent. The initial figures had shown this number had increased to 10.4 per cent.

The figures were recalculated after it was discovered that a computer error caused roughly 61,000 Canadians who reported their mother tongue as French to instead be counted as English speakers.

The error was primarily limited to French speakers in Quebec who submitted incomplete census filings.

Boxes for language were placed in a different order on the French and English forms, but the computer program counting these forms did not take this into account.

Questions raised about numbers

Statistics Canada found the mistake after questions were raised by English-language groups in Quebec that could not explain the explosion in the number of anglophones in several predominantly francophone communities in the province.

For example, it had initially been indicated that the number of anglophones in Quebec City had increased by 5,700 — growth that has now been corrected to just 100. In Rimouski, the growth of the number of English speakers was cut in half.

The order of language was flipped depending on whether the form was filled out in French or English, leading to the computer's counting error. (CBC)

But concerns that the census had similarly shown an erroneous decrease in francophones outside Quebec in certain communities, such as Sudbury, Ont., proved unfounded. The errors were limited almost entirely to Quebec.

While the share of anglophones in Quebec has declined since 2011, the absolute number grew — but by a much smaller amount. Rather than a growth of nearly 57,000 Quebecers who reported English as their only mother tongue, the number grew by only about 2,000.

As a result of the corrections, the national numbers shifted only marginally as well. The share of Canadians who are bilingual is 17.9 per cent, rather than 18 per cent. The numbers also showed slightly more francophones outside Quebec than had been the case in the initial release.

Errors are 'very rare'

In Quebec, the number who speak French most often at home was corrected to 79 per cent from the 78.3 per cent first reported. But that is still a decrease from the 80 per cent recorded in 2011.

"Errors are very rare, but they can happen," said Marc Hamel, director general of the census population program, at a technical briefing Thursday morning. "We will do a review and validation process to make sure that these processes can catch a system error down the line.

"We know that the information from the census is used for decision making and planning at all levels, says Hamel. "So we want to make sure that people can rely on these results."

Gone uncovered, the error could have had real world consequences as government funding decisions can be influenced by the census — particularly for funding related to minority languages.

And in Quebec, where language has been a delicate political issue, the initial findings reporting an increase in the use of English had some immediate political repercussions. Both the Parti Québécois and Bloc Québécois used the figures to argue for strengthened laws to protect the French language.

While the surprising numbers might have contributed to their urgency, those calls are unlikely to decrease now that the corrected numbers still indicate French is in decline in Quebec.