The limits of rational-legal authority


Easter 2014 bus-cycle accident (Image Source: James Brickwood)

The limits of rational-legal authority

One of the underlying and unquestioned aspects of modern western society is that the power of the state is derived from a rational-legal authority, that is in the Weberian sense of a purposive or instrumental rationality in pursuing some end. But what if it isn’t? What if the decisions of the state are more based on belief in how people ought to behave and how things ought to be rather than reality? What, in other words, if the lunatics really are running the asylum?

Let’s consider for a moment road safety as an archetype of such rational-legal policy, and in particular the concept of applying double demerit points across the major holiday periods. This it seems on the face of it to be a supremely rational act. There are more accidents, we wish to reduce them, therefore let us increase the sanctions for unsafe behaviour as we understand it.

So let’s look at the facts as we know them, below is a graph derived from road accident statistics for NSW showing the annual easter road toll both before and after the imposition of the double demerit scheme for the Easter long weekend.

Easter NSW road accident deaths 1970-2012

Easter NSW road accident fatalities1970-2012

As you can see from the graph the fatality rate year by year is noisy, so on the year that double demerits was introduced (1997) the accident rate was low, it continued to decrease the following year then spiked up the following. The other thing that’s obvious from the graph is that once we eliminate the noise there a consistent downwards trend in the fatality rate, unrelated to the 1997 doubt demerit scheme, the technical term for this general downward trend is Smeed’s law.

Records show that when double demerit points are in force, road fatalities are reduced. Since double demerit points were introduced in 1997, there has been a 20% reduction in fatal crashes over the relevant holiday periods.

Australia Police: About The Demerit Points Scheme

Of course this isn’t the whole story, in practice we are trying to reduce the Easter road toll relative to other periods in the same years so if we compare the normalised fatalities we see how we’re doing in a relative sense year by year. If we normalise the rates we also wash out the general trend downwards from the data, I’ll get to why that’s important in a second.

Normalised Easter fatalities 1970-2012

Normalised NSW Easter fatalities 1970-2012

Looking at the second graph, we can see that smoothed ratio of Easter/Year hovers in the range 0.01-0.015, we certainly don’t see an evidence of a significant step down in fatality rates. Of course as we’re looking at ratios we also eliminate that pesky decadal decline in fatalities. If we then split the set of normalised data points into a before and after group, then apply a Students test to the hypothesis that the average fatality rates of the two are equal we find, unsurprisingly,  that we have no reason to reject the hypothesis. Which statistically speaking is as good as it gets, number wise we actually get P(T=<t)=0.5886. So there is no evidence to indicate that double demerits works in any meaningful fashion and certainly not that there’s a decrease of 20% due to such a scheme as the Australian Police website claims.

Which brings us to the reality of the power of the state, it is unfortunately based upon actors who are boundedly rational. Politicians as an example react not to the long term trend but to the immediate political reality of Easter road tolls reported in the morning papers. Politics is also about societal choices and they in turns reflects world views, thus often policy reflects more a view of what ought to be, than reality. The problem of course is that there is always a cost to such legislative fiat, either in terms of other social goods foregone or in perverse and unanticipated effects. All of which is perhaps a caution to those who believe too much in the prescription of public policy to cure all social ills.

Based on the NSW experience my recommendation to any legislator considering implementing a double demerit scheme is simple enough, don’t. There are much better things to spend the public purse upon.


For the pre 1997 Easter statistics I drew on the National Archive Australia (Canberra Times digitised records) , while post 1997 on the Centre for Road Safety Crash statistics Online (accident statistics).