Illustration by Ryan Alexander-Tanner

AT FIRST, it just looked troubling.

Last year, after flagging a spike in officers' reported use of force against "transients" and people with mental illness—the summer of 2013 saw 112 such cases, up from 93 in the three months prior and 76 before that—the Portland Police Bureau promised, all on its own, to do a deeper review.

The spike came even as overall force was going down. So was it expanded camping sweeps? Or just a summertime influx of young travelers? The bureau's force inspector, writing in a public report last fall, urged his superiors to pull data from previous years and to diligently study the data it collected over the next several months.

It was a good sign the bureau was taking the reports seriously. They're among the lesser-known provisions of a federal reform package meant to address accusations that our cops engage in a pattern or practice of using excessive force against people with mental illness.

But suddenly, for a few hours last week, the whole affair started to look downright sinister.

The bureau's most recent use-of-force report, tallying incidents from January through March, abruptly dropped "transients" from a list of specially tracked categories. It left mental health encounters alone. Notes accompanying the data were silent on the reason why. They also kept silent on what, if anything, had been turned up in the bureau's review.

That silence, in turn, fed a series of troubling questions.

Were the numbers getting worse? Had the review found something unsavory? Or had bureau officials just forgotten the whole thing and hoped we'd all forgotten, too?

The answer from the bureau, it turns out, is none of the above.

Sergeant Pete Simpson, the bureau's lead spokesman, said analysts had a sound reason for scrapping the "transient" category: They had begun their study, but decided the category was too "vague."

Analysts had hoped to home in on force used against unsheltered, chronically homeless Portlanders, only to find that the "transient" category also wraps in people too belligerent or out of it to list an address, or homeless Portlanders who don't have an address of their own, but are nonetheless sheltered, crashing with friends or family.

Simpson says analysts are still collecting the data, just not reporting it. He says they hope to restore the category to future reports, although maybe not in time for the next report, with subcategories of "transients" added beneath.

The bureau's been struggling with a slow-going transition to a new system for writing and sharing police reports, he says. Officials hope the new system will make it easier to track and record the kind of granular data that avoids vagueness while promoting meaningful conclusions.

"We're learning as we do each of these," Simpson says. "We want to make sure we're collecting data in such a way that we present it the right way so we can have an honest conversation."

He could have stopped there, after having mostly defended the bureau's honor. But he was savvy enough to acknowledge the larger lesson: The next time the bureau makes a change that substantial, it ought to tell us why.

"If we see something, or we take something out, and there's a change," he says, "let's just explain it."