The Peak-End Rule
The peak-end rule suggests that past key positive or negative moments, or the peaks, as well as the end of that moment are the most influential factors when remembering back on past events.
This rule goes alongside a series of other psychology heuristics that although not always an accurate it is how we perceive the world around us. Instead of remembering all of the events our minds filter out lots of information and we focus on the most emotional points in that experience as well as the end.
The original study
Daniel Kahneman and Barbara Frederickson were the first to identify and research this effect in 1993 with their paper, “When More Pain is Preferred to Less: Adding a Better End”. In their study they asked participants to put their hands in cold water, putting them into an uncomfortable position. Then over 3 rounds they tested:
- 60 seconds at 14 degrees Celsius or 57 degrees Fahrenheit
- 60 seconds at 14 degrees Celsius followed by 30 seconds at 15 degrees Celsius or 59 degrees Fahrenheit
- Choose between repeating round 1 or 2
With the third option, people had a choice of putting their hands in cold water for 60 seconds and that’s it.
Or for an extra 30 seconds they could put their hand in a slightly warmer bucket of water but still not comfortable.
The obvious answers seems to be the first option but what actually happened was 80% of participants selected round 2 for the third round.
What we learn from this is that because the participants remembered that the ending was more positive with round 2 they perceived it as it being the better experience even if it’s for longer.
Further studies
There have been other studies that have found similar results since the original study. The first is a study in 1996 by Kahneman and Redelmeier where they found patients undergoing a colonoscopy or lithotripsy consistently found that those patients evaluated their discomfort based on the ending moment.
Cognitive biases
This psychology heuristic is not alone, it is forms part of the wider area of cognitive biases. This collection of biases show our way of rationalised and perceive our world even if the actual reality differs from that. We make mental shortcuts and assumptions because our we can only absorb and consider so much information before we become overwhelmed and exhausted by the decisions and choices we have to make on a day-to-day basis. Some other cognitive biases are the Barnum Effect, Bandwagon Effect or the IKEA Effect
User experience design
Now that we know the peak-end rule is based on the theory that people judge an experience at the peaks and the end how can this be applied to user experience design. We need to identify what are the most intense points are in the journey, for example if you were going to buy something this could be adding the item to the basket, or paying for the item. We also need to identify the end moment, this could be when the item has been delivered, what experience do the users have when they unwrap the item.
The peak-end rule does not mean we should only focus on those key positive or negative moments. We should look at the whole journey and make sure it is consistent and every step has been considered. Instead we should look at the peak-end rule as a way to reinforce a good experience and that those moments are opportunities to lift the experience up and becomes memorable for a good reason.
How can we identify the key moments?
The key moments are most likely going to be identified through qualitative research, this could be through user research. Alongside the user research consider mapping out the experience either with a customer journey or empathy mapping session to plot the moments as well as the emotions the participants felt during the experience.
Written by
Senior Interaction Designer and Co-Author to Tiny CSS Projects