How does the batch size of work influence the performance of a (production) process? As a child I wanted to be a mad scientist, so now as an agile coach I conducted a little experiment to find out. Repeat it on your own and post us your findings.

I have seen it at one of the numerous agile gatherings I attended and have ever since repeated it several times.

Experiment Setup

Here is the list of things and people you need for the experiment.

• a table
• 20 coins
• some cardboard
• 4 people (the workers)
• either
  • a video camera (a mobile phone would do) or
  • another 4 people (managers) with stopwatches

So here is our setup. I asked Julie (developer) and Marina (office management), Ben (our infrastructure guy), and Anselm (one of our founders) if they wanted to be part of a little game of coin flipping. Thanks again for your 10 minutes!

The Coin flipping Rules

There are just three simple rules.

• Work in batches
• Flip every coin of the batch
• Pass on flipped batch to the next worker

An experiment is no experiment without collection of some data. 🙂

What to Measure?

Let’s face it, the only thing that counts is value to the customer.

• first value delivered to customer: the time between the first coin entering the system and when it is spilled out.
• full value delivered to customer: time between first coin in to last coin out

And because we are a business we like to know the utilization of our workers.

• Utilization: the time from the first coin in to the last coin out for each worker

All set?

Flip!

Just watch the videos for an impression. The hard facts I extracted from the videos come later.

What do you think? Just by looking at it, I was amazed by the tremendous increase in throughput as batch size is reduced!

Hard Facts

Here are the results extracted from the videos by watching them over and over and over again.

It took 48,9 seconds to deliver the batch of 20 coins. On the other extreme it only took 24 seconds for the full value (20 coins) to be delivered when working in batches of 2. And the first value (2 coins) was delivered after 6 short seconds!

How faster were we compared with the one batch of 20 coins?

That means the first batch of 2 coins was delivered only 12,3% of the time it took to deliver value in the 20-coin batch. And it took less then half the time (49,1%) to deliver the full value in batches of 2 coins.

Now look at it as value over time. In the 20-coin batch, over the course of 50 seconds you would have 20 coins for 2 second (20*2 value over time). On the other extreme you would have the same value over time (even more) after 14 seconds in the batches of 2!

So, knowing that time is money :-), how much more value you would have over time with the different batch sizes? Hold your breath!

OK, with the one batch of 20 we had 20 coins for 2 seconds after 50 seconds. By reducing the batch size to 10 we got 10 coins for 8 seconds and 20 for 13 seconds. So the value over time cumulates to 340.  So by cutting the big batch in half we produced a gain in value over time of 850%!!! The smallest size of 2 would bring us to a plus of 1760%. Are you still a friend of big long running projects?

 It comes at a Cost

The cost is a higher utilization of the single worker. But from a company’s perspective this is not really bad, is it? I’d rather concentrate on a single task and get work done than being idle for 75% of my time.

Bottom Line

Smaller batches deliver value to the customer faster. Much faster. As a result there is more value over time for the customer. The utilization is also much better. So smaller batch sizes serve both your company and your customer.