Illustrating Flow and Small Batches with the Penny Game
A fundamental principle of agile and lean ways of working is the concept of flow: to continually transform items from inception to delivered value in small batches. Flow has many benefits:
- Value reaches customers and users faster.
- It enables faster feedback loops as users get new features in their hands sooner.
- Smaller batches mean reduced queues and consequently higher effectiveness.
However, focusing on flow can be counter intuitive as individuals might appear less “efficient”. One is easily mislead to believe that high efficiency (meaning here that people are fully utilized - that they are busy at all times) translates to high output and increased value delivery.
The Penny Game
The penny game (also known as the coin game) is a great agile game that illustrates effects of queues and big batches, and helps debunk the efficiency myth.
You can find instructions on how to play online, for example here: https://tastycupcakes.org/2013/05/the-penny-game/.
I am just going to give a quick overview here and instead focus on some of the outcomes and findings you get from playing.
How to Play
The penny game is usually played in 4 or 5 rounds. The task is the same across all rounds: to flip coins. Each coin represents a small piece of value-adding work.
The only thing that changes between rounds is batch size: how many coins a player flips before passing them to the next person in line. (An optional fifth round can be played introducing an extra condition that players cannot pass a coin forward if the next person is not done flipping the previous coin.)
After each round individual player times are documented as well as the time it took for the first coin and all coins, respectively, to be passed across all players.
Outcomes and Findings
When debriefing after the game, there are some key findings:
- In the first round individual times tend to vary more.
- The time it takes for the first coin to reach the end drastically reduces in later rounds (with smaller batches).
- The time it takes for all coins to reach the end is also reduced.
- Individual times tend to increase and also converge in later rounds.
At first glance it might seem counter intuitive. Despite people apparently being slower we deliver value faster! So why is this?
- In the big batch rounds coins are placed in “queues” before being passed on. It means that for a big part of the time coins are not being actively worked on.
- Individual times are better in early rounds as people can focus on their thing and potentially be very efficient. There are fewer handovers between people.
- Players are idle more of the time in early rounds, but more efficient once they do some work.
It is interesting to note that individual times converge. It makes you question how useful it is to measure individual performance vs focusing on team performance and overall cycle time.
Other things that sometimes happen:
- People get competitive and start drop coins, and “cheat” when passing coins along.
- The first player in line prepare their work to be as effective as possible.
Another Effect of Small Batches
Another effect of small batches is higher predictability - or less variance. The time variation between individual coins typically decrease with smaller batch sizes.
If you think about it, this makes sense. When you get all coins passed to you at once, you don’t necessarily pass them along in the same order you received them. While if you get one coin a a time, you are more likely to pass coins along in the same order consistently.
I would argue predictability is more important for business owners than cycle time, and with small batch sizes you become both more predictable and with shorter cycle times. An obvious win-win situation.
If you want to test this try the online penny game linked below, perfect for virtual workshops. It measures times for individual coins (something that is difficult to do running the game offline) and visualizes the result at the end of the game.
Final Thoughts
I have run the penny game many times and it is always a big success and an eye opener. I can highly encourage trying it with both development teams and stakeholders.
If you have suggestions or feedback on how to improve the online penny game version I’m all ears.
