Absolute Numbers, Proportions and License Suspensions

A few weeks ago I mentioned a new-ish Twitter account that was providing a rather valuable public service by Tweeting out absolute vs relative risk as stated in various news articles. It’s a good account because far too often scientific news is reported with things like “Cancer risk doubled” (relative risk) when the absolute risk went from .02% to .04%. Ever since I saw that account I’ve wondered about starting an “absolute numbers vs proportions” type account where you follow up news stories that compare absolute numbers for things against proportional rates to see if they are any different.

I was thinking about this again today because I got a request from some of my New Hampshire based readers this week to comment on a recent press conference held by the Governor of New Hampshire about their recent investigation in to their license suspension practices.

Some background: A few months ago there was a massive crash in Randolph, New Hampshire that killed 7 motorcyclists, many of them former Marines. The man responsible for the accident was a truck driver from Massachusetts who crossed in to their lane. In the wake of the tragedy, a detail emerged that made the whole thing even more senseless: he never should have been in possession of a valid drivers license. In addition to infractions spread over several states, a recent DUI in Connecticut should have resulted in him losing his commercial drivers license in Massachusetts. However, it appears that the Massachusetts RMV had never processed the suspension notice, so he still was driving legally. Would suspending his license have stopped him from driving that day? It’s not clear, but it certainly seems like things could have played out differently.

In the wake of this, the head of the Massachusetts RMV resigned, and both Massachusetts and New Hampshire ordered reviews of their processes for handling suspension notices sent to them by other states.

So back to the press conference. In it, Governor Sununu revealed the findings of their review, but took great care to emphasize that New Hampshire had done a much better job than Massachusetts in reviewing their out of state suspensions. He called the difference between the two states “night and day” and said “There was massive systematic failure in the state of Massachusetts. [The issue in MA was] so big; so widespread; that was not the issue here.”

He then provided more numbers to back up his claim. The two comparisons in the article above say that NH found their backlog of notices was 13,015, but MAs was 100,000. NH had sent suspension notices to 904 drivers based on the findings, MA had to send 2,476. Definitely a big difference, but I’m sure you can see where I’m going with this. The population of MA is just under 7 million people, and NH is just about 1.3 million. Looking at just the number of license drivers, it’s 4.7 million vs 1 million. So basically we’ve got a 5:1 ratio of MA to NH people. Thus a backlog of 13,000 would proportionally be 65,000 in MA (agreeing with Sununu’s point) but the 904 suspensions is proportionally much higher than MAs 2,476 (disagreeing with Sununu’s point). If you were to change it to the standard “per 100,000 people”, MA sent suspension notices to 52 people per 100,000 drivers, NH sent 90 per 100,000.

I couldn’t find the whole press conference video nor the white paper they said they wrote so I’m not sure if this proportionality issue was mentioned, but it wasn’t in anything I read. There were absolutely some absurd failures in Massachusetts, but I’m a bit leery of comparing absolute numbers when the base populations are so different. Base rates are an important concept, and one we should keep in mind, with or without a cleverly named Twitter feed.

Math aside, I do hope that all of these reforms help prevent similar issues in the future. This was a terrible tragedy, and unfortunately one that uncovered really gaps in the system that was supposed to deal with this sort of thing. Here’s hoping for peace for the victim’s families, and that everyone has a safe and peaceful Labor Day weekend!

 

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