These terms are often used interchangeably but are two different approaches to how you design your products and services. A recent paper on Co-production with Autistic adults3 communicates the differences using this tiered diagram to indicate the levels in which participants are involved:
In Co-design: your participants are treated as equals and have equal say in decision making of the project goals and outcomes.
Participatory design: users give input but ultimately you are the decision maker and hold the power.
A great example of co-design was a project with ARCScotland where young people were asked to design a consultation for other young people. The data from the consultation was given to the young people which they used to inform the design of a Software tool. The young people were given feedback on the design of the consultation but it was their final decision.
In a research context, Sue Fletcher-Watson1, from the University of Edinburgh sought an Autistic mentor to get input into research before the research projects started. She wanted to get input at the grant-writing stage. This approach gives the community the ability to shape the direction of research early on.
What should I use if I am building technology?
The size of a product can make a difference. If the product is small participatory design with short iteration cycles is still a good approach to testing your product to get feedback to ensure you are building the right tool.
If you have a longer project co-design should reduce the number of iterations a product requires by getting input at an earlier stage. The process enables you to build better relationships with users, learn how they think and increase the opportunity of finding novel and innovative solutions by introducing new perspectives. It reduces the risk of designing the wrong solution from the outset and the risk of investing resources into the wrong place.