The revelation that Canadian police are routinely mislabelling sexual-assault complaints as "unfounded" – a classification that means no crime was committed – is shocking.

This cold clerical error is depriving the public of an accurate picture of the magnitude of sexual assault in Canada. Worse, the outmoded policing behind it is robbing victims – the vast majority of whom are women – of a consistent application of justice, and making their difficult choice to press charges even more fraught.

An investigation by The Globe and Mail has found that police classify an average of 5,500 sexual-assault complaints as unfounded every year. That means these cases are not included in statistics about sexual assault, which in turn inflates the already low percentage of complaints that lead to charges.

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Unfounded: Police dismiss 1 in 5 sexual assault claims as baseless, Globe investigation reveals

Interactive: Will the police believe you? Compare unfounded sex assault rates across Canada

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The investigation also reveals a shocking disparity in police practices. In Saint John, police decided that fully half the complaints they investigated from 2010 to 2014 were unfounded. In London, Ont., the rate was 30 per cent. But in Toronto, it was just 7 per cent.

Overall, the national average of 19.4 per cent is dramatically higher than the unfounded rate for other violent crimes – for physical assault, it is 10.8 per cent.

Experts blame inconsistent police training for the discrepancies. One study showed that complaints can get categorized as unfounded as a result of an officer's poor interviewing and investigation skills. Police in London, Ont., have now reclassified one unfounded case examined by The Globe as a founded allegation, after they took a second look at the video of the woman's interview and discovered the detective who questioned her pushed her to agree that the sex was consensual.

It is widely believed that fewer than one in 10 victims of sexual assault will actually come forward with a complaint. Those whose cases get to trial face a gruelling process and a low chance of seeing a conviction. Unfairly dismissing their complaints as unfounded only adds to the sense that the system is weighted against sexual-assault victims from the start.

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Police forces, like those in Toronto, Winnipeg and Surrey, that have shed outdated methods and attitudes have reduced their unfounded rates to single digits. There is no excuse for any other force that fails to do the same. Fairness demands it.