tag:blogger.com,1999:blog-2830084253401570472.post3530026799889320179..comments2024-03-18T15:42:43.140+13:00Comments on Offsetting Behaviour: Finding the denominatorEric Cramptonhttp://www.blogger.com/profile/15831696523324469713noreply@blogger.comBlogger4125tag:blogger.com,1999:blog-2830084253401570472.post-57364018561044660362012-12-21T14:22:23.688+13:002012-12-21T14:22:23.688+13:00When I was out, the only non random bits were that...When I was out, the only non random bits were that taxis were waived through and everyone parking or turning quickly on seeing the checkstop were hit. Otherwise it seemed based on stuff orthogonal to drinking.Eric Cramptonhttp://offsettingbehaviour.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-2830084253401570472.post-63426163069019909252012-12-21T11:02:20.134+13:002012-12-21T11:02:20.134+13:00Downstream impact is interesting. I agree with yo...Downstream impact is interesting. I agree with you, that's a negative impact on people who were law abiding even under the mooted new law.<br /><br />On selection, my concern is that at high volume times the police in some places appear to pull over only a subset of the vehicles. What isn't clear to me is whether this is genuinely random - so they do all the cars in their queue, then they stop the next 20 cars irrespective of who they are, or whether they pull out specific cars based on "intuition" as to who looks dodgy. If the latter, then if we presume that police intuition has some sort of basis in fact, they are more likely to be pulling over cars of people who have been drinking or are otherwise dodgy.PaulLnoreply@blogger.comtag:blogger.com,1999:blog-2830084253401570472.post-23962654751736704882012-12-20T16:37:45.748+13:002012-12-20T16:37:45.748+13:00I'm also expecting that #4 is what obtains. Bu...I'm also expecting that #4 is what obtains. But who knows. That's what makes it fun. <br /><br /><br />The night I spent out with the police was really instructive on how that data gets collected; I'd have been a fool not to do it even had I known that MoT was already gathering the data. My current worries:<br />1) The first-round breath screening devices do not seem all that sensitive for low-level drinking. Many drivers admitting to have had something to drink showed up on those initial screens as having had no alcohol (presence of alcohol on the initial screen has you blow in the tube for the finer reading of 0, 0-250, 250-400, >400). Most of those drivers would have been in the 0-250 mcg range, but maybe some were in the 250-400 range. That would have me underestimating the number of drivers affected.<br />2) MoT's data gathering was on Friday and Saturday nights - relatively high drinking times. But so long as I restrict things so the range of accidents (day/time) matches the days of data collection, I should be ok. <br />3) Agreed on upstream impact, but I also worry about downstream impact. Suppose that I target 240 trying to avoid accidentally hitting 400. What do I target to avoid hitting 250? There will have to be a reasonable consumption drop among those in the 0-250 range, but it's not going to be easy to reckon how much.Eric Cramptonhttp://offsettingbehaviour.blogspot.com/noreply@blogger.comtag:blogger.com,1999:blog-2830084253401570472.post-6801357818957620202012-12-20T14:56:09.884+13:002012-12-20T14:56:09.884+13:00Fantastic - this is exactly what we need to have a...Fantastic - this is exactly what we need to have a sensible decision that doesn't rely on some public health types asserting "people are drinking, and some of them have accidents, clearly the problem is the drinking."<br /><br />I think there are a few possible answers that could come out:<br />1. There are no people driving in the 0.05-0.08 range. Unlikely<br /><br /><br /><br />2. There are people driving in the 0.05-0.08 range, and their proportion of accidents is less than their overall proportion of the drivers. In this case, we should force everyone to drink 0.05-0.08 before they drive. :-)<br /><br />3. There are people driving in the 0.05-0.08 range, and their proportion of accidents is roughly the same as their overall proportion of the drivers. In this case, we probably should do nothing about the law.<br /><br />4. There are people driving in the 0.05-0.08 range, and their proportion of accidents<br /> is higher than their overall proportion of the drivers, but the increased accidents (assume 1-2 per annum) is lower than the benefits that the drivers (assume many hundreds of thousands) get from being able to have one or two drinks (including their health benefits). In this case, we probably should do nothing about the law, but it's hard to explain to many people (would it be rude to describe them as stupid people?)<br /><br />5. There are people driving in the 0.05-0.08 range, and their proportion of accidents is higher than their overall proportion of the drivers, and the increased accidents (assume more than 2 per annum) is higher than the benefits that the drivers (assume many hundreds of thousands) get from being able to have one or two drinks (including their health benefits). In this case, we probably should change the law to reduce the limit.<br /><br />Other things to watch out for:<br />- selection bias. Do the police select for "random breath tests" those who are more likely to have been drinking? (i.e. does everyone get tested, or some subset that the Police select)<br /><br />- is there an upstream impact - does pushing down the limit 0.05-0.08 also drag down those drinking at higher levels? And if so, is it morally reasonable to change the rules for those who are doing nothing wrong so as to impact those who are already breaking the law?PaulLnoreply@blogger.com