Angry in the Great White North

The disappearance of nine-year-old Cedrika Provencher of Trois-Rivieres is being considered by most as an abduction:

But by Saturday, with no solid leads to go on, police focused their efforts on investigating the circumstances regarding her disappearance.

To date, the most promising lead came when several other parents from the area told police their children had been approached by a suspicious man in the days prior to Cedrika's disappearance. On Thursday, a woman told police a man had approached her 13-year-old daughter and asked if she would help him find his dog.

Earlier reports described the man as being in his mid-30s with short dark brown hair, standing about 5 feet, 10 inches tall and weighing 150 pounds.

But Gendron says police could not get a clear description of the man. They are, however, looking into the files of several registered sex offenders who live in the area.

Several registered sex offenders? What does that mean? Three? Five?

Ten?

Certainly not more than that.

Of course, the authorities won't tell us exactly what constitutes "several" sex offenders. For that we have to depend on sources:

Other residents in the area say they have seen a man hanging around, others have said a man has approached their children asking them various questions.

Investigators are now questioning known pedophiles in the Trois Rivieres area. Sources say there are about 75 of them.

Seventy-five? Seventy-five?!

Not all registered sex offenders are pedophiles. But then we don't know, do we? Until now, I didn't know 75 sex-offenders were in Trois-Rivieres.

Imagine the difficulty facing the police. That's up to seventy-five interviews to conduct in as short a time as possible, even as the hours go by without sign of Cedrika. Each is a potential suspect. Each will have to provide alibis that will have to be checked out. More resources will be expended tracking down the registered sex-offenders who are not immediately available. Is he at work, or buying groceries, or visiting a neighbour, or is he on the run with Cedrika? Out of a population of seventy-five, there will certainly be a few who are not found on the first try, distracting the police hoping that there is some significance to the fact that no one is answering the door.

How many of the 75 are going to required detailed investigation? Can't really say, but engineers use a rule of thumb called the 80-20 rule. It tells us that in any expenditure of effort, 20% of the tasks will require 80% of the effort. Putting it the other way around, 80% of the tasks will be quickly taken care of. So 80% of the 75 sex-offenders will quickly be determined to be of no interest in this case (rock-solid alibi, wrong sort of profile with regards to sex crimes, no opportunity or means, and so on). That means 20%, or 15 registered sex-offenders, will for one reason or another require detailed investigation by the police.

That's why the number 75 seemed so large to me. My gut tells me that a large sample size like that will result in a significant number for the police to investigate in detail.

Fifteen sex-offenders who cannot immediately be dismissed as suspects? Even if the 80-20 rule engineers use is really 90-10 for police work, that still leaves eight sex-offenders splitting the resources of the police in this investigation.

Of course, maybe none of these 75 are involved. But of the eight or fifteen of interest, perhaps one has a suspicion about what has happened to Cedrika. Maybe he knows of a new pedophile in the area. To admit that, though, might require admitting to breaking the conidtions of his reliease, such as visitng internet websites forbidden to him. That would require even more effort from the police to extract that information.

All that effort applied to eight to fifteen serious suspects.

Of course, it wasn't until Cedrika Provencher went missing that parents in Trois-Rivieres realized 75 sex offenders in their midst.