Behaviour Change

PROPAGANDA FOR CHANGE is a project created by the students of Behaviour Change (ps359) and Professor Thomas Hills @thomhills at the Psychology Department of the University of Warwick. This work was supported by funding from Warwick's Institute for Advanced Teaching and Learning.

Tuesday, April 24, 2018

UseLESS Plastic

The problem of plastic

Plastic consumption has become an increasingly large problem over the past decades. In 2017 there was 6.3 billion metric tonnes of plastic waste (Parker, 2017) and it has been reported that one of the largest sources of this waste is from drinks bottles. Trowsdale, Housden, and Meier (2017) reported that 480 billion plastic bottles were sold in 2016 which is the equivalent of 1,000,000 plastic bottles being sold every minute!

The Marine Conservation Society (2017) found that since 1994, plastic litter has increased by 180%. This growing issue has become even more apparent since China recently placed a ban on importing plastic waste from countries including the UK. In previous years, Britain shipped roughly 500,000 tonnes of plastic to China for it to be recycled, but this will no longer be possible (Harrabin, 2018). There is a growing concern that Britain will be unable to deal effectively with the excess plastic and therefore it is more important than ever to start reducing plastic consumption whenever possible.  

There has been extensive media coverage about plastic waste consumption in the news. For example, the Guardian have stated that the amount of plastic which is produced every year is roughly the equivalent of the entire weight of humanity (MacArthur, 2017).  See Figure 1. for the increase in global annual plastic production.

Figure 1.- Global annual plastic production increase in million tons.

The government are on board to help reduce plastic waste. Recently, new measures have been proposed which suggest alternative ways in which the country could prevent levels of wasted plastic consumption from worsening.  For example, the government have suggested charging each customer a 25p levy for each plastic cup they purchase. Hopefully this extra cost would encourage others to cut down on individual plastic waste and the revenue generated could be put towards maintaining facilities which ensure other disposable cups are recycled (Environmental Audit Committee, 2018). Another measure suggested is introducing a deposit return scheme which involves individuals paying a small sum of money which will be refunded back to the individual once the bottle has been returned. This already takes place in several other countries including Germany and the success of this scheme can be highlighted by the fact that Germany has now reached a recycling rate of 99% (Laville & Zhou, 2017).

In the UK alone, 35.8 million plastic water bottles are used every single day on average (Refill). However, according to the website Refill, if just 1 in 10 people refilled their bottle once a week, there would be 340 million less plastic bottles a year. Therefore, we thought that using a reusable bottle would be feasible for students and staff to do and would have large wide-reaching benefits.

How we solved the problem:

Stage 1: Where to start

To get the ball rolling we decided to plan a meeting with Tony Howard (Director of Food and Retail Strategy) and David Chapman (Sustainability Champion). In this meeting we incorporated two key persuasion tactics. Firstly, we used the ‘Just Ask’ principle. The Just Ask principle suggests that if you ask for something, you are likely to get what you asked for (Hills, 2014).

Secondly, we attempted the ‘Door-in-the-Face’ tactic. This technique states that one should demand a large favour which will normally be rejected, but will create a feeling of indebtedness increasing the chance that a smaller request will be accepted (Pratkanis, 2007). Moreover, due to the contrast effect, the smaller request will now appear more attractive as it will be compared to the previous large request (Miller, 1974). We were aware that the Door-in-the-Face tactic can backfire if future negotiations are likely; if the people you’re negotiating with realise that you’re using this tactic, they may see you as less trustworthy and be more likely to switch to a different person to collaborate with in the future (Wong & Howard, 2018). However, as we only needed to negotiate once for our funding, we decided that the door-in-the-face tactic would be appropriate in this case.  We decided that we would ask for funding for 2000 reusable water bottles. This was our big request. Why 2,000? We needed to create a social norm. We hoped that if people saw their peers with our water bottles, they would want one too and would create an expectation that using reusable water bottles on campus is the norm rather than using plastic water bottles. Creating a social norm will also create social pressures to conform which will encourage long-term use of the bottles (Prakanis, 2007).  We did not expect Tony and David to accept our big request, so we had a backup (to ask them to remove plastic straws from SU outlet bars and only give them to customers who directly request them). This would have been our small request as it would cost nothing. However, Tony and David loved our idea to give out reusable water bottles and were happy to help. Tony even committed to getting rid of single use plastic cups from water fountains. This meant that we didn’t get chance to offer our small request as they accepted our big request! Note: we did manage to reduce plastic straw consumption in Leamington Spa though…(see mini project on plastic straws at the end of the page).

2. Securing Funding

Having decided how many bottles we would need (2,000), we then had to research how much they would cost and where we would get the funding from. We received various quotes of around £1-£2 per bottle. David helped us get in touch with the SU in order to apply for funding. We applied for £2,000 from the University Environment and Sustainability Fund in the hope that we could get 2,000 bottles for £1 each. We did not expect to receive the full £2,000 but decided to ‘Just Ask’ for it anyway. We then had to attend a meeting with the Development Exec to answer questions about our application. The board rejected our request of £2,000 but decided to grant us £500 instead. We believe that asking for £2,000 anchored them on a high number. This meant that the amount of money they gave us was still generous. If we had asked for a lower number, say £500, they might have anchored on this and offered us a lower amount. Anchoring is a cognitive heuristic which explains how judgements can be influenced by completely random numbers without individuals being aware the numbers had influenced their judgement (Wilson, Houston, Etling, & Brekke,1996). Our £2000 may have acted as a base value for the Development Exec and helped us to secure a funding of £500. After securing the £500 funding from the SU, we received a message from Tony stating that he’d managed to secure us full funding for 2,000 reusable metal water bottles. We added the £500 from the SU to the funding from the University in order to print both the SU and University logos onto the bottles.

3. Promoting our campaign

Once we had secured funding for the 2,000 bottles we could promote our campaign. We designed posters to put up around campus and ‘Just Asked’ various people to post on Facebook/ email students in order to get the word out.

The poster we designed used the scarcity principle in order to encourage staff and students to come and collect their bottles quickly before they all ran out! The poster said "Limited number of bottles available: Once they’re gone, they’re gone!". We expected that when people saw there were a limited number of bottles available, they would rush to get theirs before it was too late! When items are scarce, they are highly sought after. The concept of scarcity was demonstrated in a study by Brehm and Weintraub (1977), where they found that less accessible items were more desired when compared to items that were more accessible. Another study by Van Herpen, Pieters and Zeelenberg (2014) found that scarce products were rated more unique and exclusive than products that were not scarce, leading to more people choosing the scarce product over the non-scarce one. Highlighting the scarcity of the bottles would therefore increase their desirability and value, making people want one more.

We also used rhetorical questions in our poster, such as “Did you know London alone uses 7.7 billion plastic bottles a year?” According to Burnkrant & Howard (1984), rhetorical questions can increase processing of a message which results in increased persuasion when the message is strong, as ours is.

4. Giving out the bottles

Our main persuasion tactic when giving out our FREE reusable bottles was the reciprocity principle. Over the course of two days, we gave away all 2,000 bottles. We gave the bottles away for FREE so people would download a free app called ‘Refill’ designed to show them where they can fill up their water bottle on campus and parts of the UK. When we are given something for free we feel obliged to repay the favour as we do not like to feel indebted to people (Cialdini, 2007). The reciprocity principle is demonstrated in a study by Burger, Sanchez, Imberi and Grande (2009). A confederate in this study asked all the participants to fill in a questionnaire and return it in a few days, whilst also giving half the participants a free water bottle. The questionnaires were either anonymous or non-anonymous. When the participants received a favour (the water bottle from the confederate), they were more likely to return the questionnaire than when they didn’t receive a favour, regardless of whether the questionnaires were anonymous or not. This was an important finding for our project as downloading the app at a later date would be anonymous; we would not know who had downloaded the app and who hadn’t. Whilst we trusted that people would download the app later, we encouraged participants to download the app straight after taking a free water bottle because previous research has found that people are less likely to return a favour as the length of time increases between the initial favour and the chance to reciprocate (Burger, Horita, Kinoshita, Roberts & Vera, 1997). For example, Burger and colleagues (1997) found that participants were more inclined to repay a favour when they were asked 5 minutes after they had received a free drink from the confederate than 1 week later. It was difficult to measure how many people actually downloaded the app (although some people did it straight away in front of us, which is evidence that the reciprocity principle worked!). However, it is clear that the app is becoming much more widely used across campus, likely due to us asking people to download it. Before the launch of our campaign, there were only two refill sites on campus. There are now seventeen (and counting)! We hope that the app will encourage people to continue to use their reusable water bottles.

Figure 2. Day 1 of giving out the FREE water bottles in Rootes Grocery Store

We also invoked the principle of written commitment. We asked people to sign a statement that said, “I will use my reusable water bottle as much as possible, and will therefore be reducing plastic waste and helping to save the environment”. This principle is demonstrated in a study by Deutsch and Gerard (1955). In this study, individuals were split into three groups and asked to make estimates about the length of lines. One group was asked to keep their estimates to themselves (in their head) and not write them down. The second group was asked to write their estimates down but not show anyone else. The third group was asked to write their estimates down and show the experimenter. The experimenters then told the participants that their estimates were incorrect and the participants were given the chance to change their estimates. The researchers were interested in how many participants changed their minds once receiving disconfirming evidence. Interestingly, the group most resistant to changing their minds were those who had written their estimates down and shown the experimenter, highlighting the power of written commitments. When people signed our pledge they committed to using their water bottle as much as possible. We hope that their intention to use their water bottle as much as possible will transform into actual behaviour of reusing their water bottle.

Another principle we used when giving out the bottles was social proof. We used A3 sheets of paper to collect signatures for our pledge in the hope that when people saw others have pledged to use their bottles as much as they can, they would too. Cialdini (2007) stated that people are more likely to conform with an action when they have a lot of proof that it is the correct thing to do. Moreover, Burger and Shelton (2011) highlighted the power of social proof in their study. They found that simply placing a sign stating, “more than 90 percent of the time, people in this building use the stairs instead of the elevator” resulted in the number of people using the elevator falling by 46%. We kept the full sheets of paper on the table for people to see (see Figure 3). By laying out the completed signature sheets, people had proof that others are using reusable water bottles and thus increased the likelihood that they too would take and re-use a bottle.

Figure 3. The ten A3 sheets of paper, full of signatures of individuals committing to using their water bottles.

A visual representation of the different stages of our project


We are confident that our project was a huge success. Warwick University have committed to removing single-use plastic cups from water fountains and 2,000 staff and students at the University of Warwick have committed to using reusable water bottles. If we use what we know from the 'Refill' organisation, this means that if all 2,000 staff and students fill up their reusable bottle once a week, there will be approximately 105,000 less plastic water bottles in circulation every year. That's quite an achievement...

Mini Project: How we reduced plastic straw consumption...

It is not a rare occurrence to be asked if you want a plastic straw when ordering a drink at a bar. Many people do not understand that answering "yes" to this question makes them a key contributor to the devastating amount of plastic being used and dumped in the ocean every day. Over 500 million straws are used every day in the US (Parker, 2018), making single-use plastic straw consumption a serious issue. Plastic straw consumption is such a pressing issue that the UK Environment secretary Michael Gove has urged the UK government to ban the sale of plastic straws (Independent, 2018).

To reduce commercial plastic straw consumption, we created a pledge and asked eight local business to sign it. The pledge stated "we will only give out plastic straws to customers who directly request them". When showing the managers the pledge, they saw the list of other businesses who had signed it. Here we enforced the technique of  social proof; people like to follow what others see as correct (Cialdini, 2014). When the business managers saw that other local companies had signed our pledge, they too felt obliged to sign it. Therefore, the Leamington business owners likely signed the straw petition as they believed that if others thought it was the correct thing to do, then they should too. Furthermore, a previous study looking at social proof found that people are more likely to conform to what others have done if the others are similar to them (Hornstein, Fisch & Holmes, 1968). The Leamington Spa business owners were likely to sign our petition as all the previous signers were similar to themselves.

Eight business signed our pledge to reduce plastic straw consumption. Like our water bottle campaign, we also used written commitment. Written commitment has proven to be an effective method to get people to behave consistently with their prior beliefs (Levy, 1997). We hoped that the businesses would stick to their promise and only give straws to those who have asked for one. Those who didn’t sign the pledge already had steps in place to reduce plastic straw consumption which is great!


We would like to say a huge thank you to Tony Howard (Director of Food and Retail Strategy) and David Chapman (Sustainability Champion) who helped us along the way. From securing funding to suggesting ways we can make our campaign more effective to sourcing environmentally friendly bottles. We would also like to thank Megan Holland (Marketing Officer) for working behind the scenes with the marketing of our campaign. Finally, we would like to thank the SU for their contribution to our funding. It would not have been possible to do this project without all of these individuals.

By Lottie Devey Smith, Hattie Goodhart and Rebecca Jacobs.


Burger, J. M., Horita, M., Kinoshita, L., Roberts, K., & Vera, C. (1997). Effects on time on the norm of reciprocity. Basic and Applied Social Psychology, 19, 91-100.

Burger, J. M., Sanchez, J., Imberi, J. E., & Grande, L. R. (2009). The norm of reciprocity as an internalized social norm: Returning favors even when no one finds out. Social Influence, 4, 11-17.

Burger, J. M., & Shelton, M. (2011). Changing everyday health behaviors through descriptive norm manipulations. Social Influence, 6, 69-77.

Burnkrant, R. E., & Howard, D. J. (1984). Effects of the use of introductory rhetorical questions versus statements on information processing. Journal of Personality and Social Psychology, 47, 1218-1230.

Cialdini, R. B. (2007). Influence: The psychology of persuasion. New York: Collins.

Cialdini, R. B. (2014). Influence: Science and practice. Harlow, Essex: Pearson Education Limited.

Environmental Audit Committee. (2018). Disposable Packaging: Coffee Cups. UK: House of            Commons.

Eriksen, M., Lebreton, L. C. M., Carson, H. S., Thiel, M., Moore, C. J., Borerro, J. C., Galgani, F., Ryan, P. G., & Reisser, J. (2014). Plastic pollution in the world’s oceans: more than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea. Plos One, 9, 1-15.

Harrabin, R. (2018, January 1). UK faces build-up of plastic waste. The BBC. Retrieved from:   

Hornstein, H. A., Fisch, E., & Holmes, M. (1968). Influence of a model’s feeling about his behavior and his relevance as a comparison other on observers’ helping behavior. Journal of Personality and Social Psychology, 10, 222-226.

Laville, S., & Zhou, N. (2017, June 29). Could a money-back scheme clean up the UK’s                       plastic bottle plague? The Guardian. Retrieved from:                                         

Levy, R. L. (1977). Relationship of an overt commitment to task compliance in behavior                   therapy. Journal of Behavior Therapy and Experimental Psychiatry, 8, 25-29.

MacArthur. (2017, June 28).  A million bottles a minute: world’s plastic binge ‘as dangerous as climate change’. The Guardian. Retrieved from:                         

Marine Conservation Society. (2017, November 30). Beach litter rises 10% in the UK,                        shocking report reveals.

Parker, L. (2017, July 19). A whopping 91% of plastic isn’t recycled. National Geographic.                Retrieved from:

Parker, L. (2018, February 23). Straw Wars: The Fight to Rid the Oceans of Discarded                         Plastic. National Geographic. Retrieved from:


Trowsdale, A., Housden, T., & Meier, B. (2017, December 10). Seven charts that explain the           plastic pollution problem. The BBC. Retrieved from:

Tversky, A., & Kahneman, D. (1974). Judgment under uncertainty: Heuristics and biases. Science, 185, 1124-1131.

Van Herpen, E., Pieters, R., & Zeelenberg, M. (2014). When less sells more or less: The scarcity principle in wine choice. Food Quality and Preference, 36, 153-160.

Watts, J. (2018, April 18). UK to ban sale of plastic straws and drink stirrers that blight the country’s seas and rivers, ministers say. The Independent. Retrieved from:

Wilson, T. D., Houston, C. E., Etling, K. M., & Brekke, N. (1996). A new look at anchoring   effects: basic anchoring and its antecedents. Journal of Experimental Psychology: General, 125, 387- 402.

Wong, R. S., & Howard, S. (2018). Think twice before using door-in-the-face tactics in repeated negotiation: Effects on negotiated outcomes, trust and perceived ethical behaviour. International Journal of Conflict Management, 29, 167-188.


  1. Replies
    1. Thank you so much Giuseppe! Glad to see yours was really successful too!


Note: Only a member of this blog may post a comment.