How can people’s behaviour be changed?

One of our regular contributors, Phil Hall, looks at the success of the recently-introduced plastic bag charge in England, and asks if there are lessons for the completion of the UK’s stalled metric changeover.

It has been reported recently that the campaign to reduce the number of disposable plastic bags in shops has been a success¹. This is good news and there are a some interesting features:

  1. Prior to the introduction of the 5p charge, surveys showed 50% support for the initiative. Afterwards that support rose to 75% ²
  2. An environmental psychologist³ said that it worked because it only required a small change in behaviour.
  3. It followed a lead from politicians.

It is also the case that the legal change was a European initiative, which begs the question as to whether the UK would have done it independently.

So what has this to do with metrication? Well it’s just an observation that when a case is strong enough it doesn’t have to be based on popularity. Metrication is probably not as popular as the reduction in the use of disposable plastic shopping bags but it wouldn’t be hard to attain it with a sensible campaign from the right quarters.

Adopting the kilometre in place of the mile, or say the kg instead of the lb is not much of a hardship. Surely worthwhile if it gets rid of the irritating issues such as of having to use two systems of measurement while being familiar with neither or wasting school children’s time teaching conversions when one system of measurement is all they should need.


  2. A BBC TV news reporter spoke to an Environmental Psychologist who quoted the figures.
  3. As in reference 2, spoke about behavioural aspects.

Author: UK Metric Association

Campaigning for a single, rational system of measurement

6 thoughts on “How can people’s behaviour be changed?”

  1. The reason this may have worked is there is a charge for the bags. If they were free and people were asked to voluntarily reduce their use, I would say they would not.

    Something similar has to happen with metrication. Shops could be required to charge more for quantities asked in pounds or better yet to offer a discount if certain gram sizes are requested. Like 500 g for the price of 450 g.

    I don’t know how a fee would work for road signs, but maybe there doesn’t have to be any. Just making it clear in the law that metric road signs are perfectly legal would give local authorities the incentive to start metricating. It would happen automatically as a result.


  2. It takes time to change people’s opinions, but just like children can’t work down pits and women can vote. we must never force people to change but show a logic in why we need to change.


  3. @Daniel:

    Regarding road signs, perhaps if the financial cost of having imperial units could be made to impact consumers directly. One way of doing this is for car manufacturers to either highlight or even protest to the government that vehicles with dual units cost more than having just metric units (assuming they do of course – maybe not, but I can’t imagine there is no cost involved).

    If manufacturers made it clear that vehicles in the UK cost, say, £25 more than metric only vehicles, that may just be the impetus for consumers to demand that our road signs should be converted. Even sweeter, I wonder if manufacturers might even help fund the (one time) conversion costs in return for the long term cost savings? Just a thought.


  4. Lead by example comes to mind. That is the most effective.
    If those in power refuse to use metric then so do most of the followers, there can be no other outcome. The BBC news seems to have reverted to using mostly Imperial. In the recent reports from Iraq the presenter used km the first couple of nights, after that she started using miles. So once again I take some convincing that this is a ‘free choice’ of a presumably metric orientated presenter to suddenly see the light and start using Imperial. Exactly the same with the ESA mars lander, the first report or two were all metric as issued by ESA, later they got translated into miles and mph.
    Any move by government to start adopting metric by deed, with or without legislation, would I am sure bring about a fairly rapid change by the media, then by the public.
    Certain tabloids of course would take a bit longer.


  5. The use of “miles” seems to be the ubiquitous offense when it comes to the persistence of Imperial in the media and everyday usage. As the experience of Ireland teaches us (as well as that of Canada, by the way), once road signs get converted, “miles” pretty much disappears.


  6. Just saw today an interesting confirmation of the positive effect on metrication by the metrication of road signs when I watched a report about COP22, the climate change conference currently going on in Morocco.

    Mary Robinson, former President of Ireland, was being interviewed about why COP22 was important, how the world could react to a climate change denier (Trump) being in the White House, etc. She spoke freely and easily about the 2 degree Celsius upper limit agreed to with the additional tighter target agreed to in Paris of 1.5 degrees, the possible rise in the oceans of 1 meter and what that will do to coastal communities, etc.

    What struck me was how she used metric as easily and naturally as any Australian would. Most impressive and greatly heartening.

    Contrast this with the miserable editing policies at the BBC (even the so-called “World” Service, both radio and web site) where Imperial continues to appear regularly, and sometimes even in first position and (incredibly) in some cases even all by itself with no metric whatsoever!

    It’s not clear what will ever give us a DfT ready to recommend conversion of road signs in the UK with a reasonable cost estimate (please just ask the Irish!). However, should that day ever come, it’s a fair bet that Imperial will finally (and fairly quickly) go by the wayside (where it certainly belongs).

    (As for the USA, well … I’m too depressed to even speculate on that one for the moment. Stay tuned, I guess, lads and lasses!)


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