New research reveals systematic differences in the failure rate of the MOT across postcodes: a car of the same type, after controlling for age and mileage, is more likely to fail in some postcodes than others.
What’s more, a car of the same type and age, and controlling for mileage, is typically less likely to fail its MOT on Friday than on Monday. And silver cars are less likely to fail the test than white ones.
These are among the findings of a study by Shaun Hargreaves Heap and Oleksandr Talavera, to be presented at the Royal Economic Society's annual conference at the University of Warwick in April 2019. They analyse data from a sample of about 121 million MOT tests during the period from 2005 to 2013.
The researchers’ initial focus was on ‘street-level bureaucrats’ – the agents of the state who deal directly with the general public when a policy is implemented. These are typically public employees, but with the trend towards the privatisation of government services, many are now private employees.
To some degree, street-level bureaucrats have discretion in what they do. The question addressed by this study is whether the exercise of discretion by one such group – MOT testers – affects systematically the implementation of vehicle roadworthiness standards.
The researchers’ test for the existence of discretion turns on whether the probability of a car failing the MOT test depends systematically on non-MOT feature of vehicles. Based on a sample of about 121 million MOT tests during 2005-2013, the study finds evidence that MOT testers do exercise discretion in this sense.
First, the data reveal systematic differences in the failure rate across postcodes. A car of the same type, after controlling for age and mileage, is more likely to fail in some postcodes than others and these differentials persist over time.
This variation is worrying from a policy perspective, especially as these differences are quantitatively significant and are negatively associated with postcode differences in the occurrence of road traffic accidents.
Second, the researchers document patterns in failure rates that seem shared across postcode areas and which do not have anything to do with the requirements of the test itself. For example, a car of the same type and age, and controlling for mileage, is typically less likely to fail an MOT on Friday than on Monday.
Furthermore, silver cars are less likely to fail the test than white ones. There is nothing in the test that makes the standard for passing different on Fridays or for silver cars.
The existence of a ‘weekend effect’ of this kind has also been noticed in financial markets. It could arise in MOT testing for the same reason: that proximity to the weekend encourages a more optimistic result on Fridays for testing than does the prospect of a week of work on Monday.
This evidence of something similar in a very different activity is important because it suggests that the day-of-the-week behavioural effect in decision-making may be more widespread than has hitherto been recognised.
The grey/silver colour behavioural bias is important because, to the knowledge of these authors, it has not been observed before and does not fit in any obvious way with what is known about the physiology or psychology of colour.
For example, it cannot be related to Goldstein’s (1942) wavelength theory of colour emotional arousal. This theory predicts the major differences are between red and yellow (arousing) and blue and green (calming). This is not what is found here. Silver and grey contain all the colours: they just have less light than white.
VEHICLE ROADWORTHINESS: Your car is less likely to fail its MOT on a Friday than a Monday by Shaun Hargreaves Heap (Kings College London) and Oleksandr Talavera (University of Birmingham
Goldstein, K (1942) ‘Some experimental observations concerning the influence of colors on the function of the organism’, Occupational Therapy and Rehabilitation 21: 147-151.
Professor of Political Economy at King’s College London
Professor of Financial Economics at University of Birmingham