A few people have commented on twitter about Deming’s contention that 95% of what you see is down to the system and only 5% is down to the individual. They keep asking where he got the 95% from.

He used to run a course, which is still available as a book: Four Days with Doctor Deming. At the very beginning of the course he invited the participants to play a game with red and white beads. There’s a youtube video describing it here. The you pick up beads with paddles, the workers are rewarded for picking up white beads and punished for red, even ‘fired’.

When you look at the numbers for the game it turns out that the workers have no control over the physical process of selecting the beads. In one trial someone may do really well, and in another badly and get ‘fired’.

In statistics we use confidence limits. When we take a new measurement you look at it and can perform some analysis to say how likely it is that the measurement falls inside the existing set of measurements. Typically we use the 95% confidence limit to say that there is a one in twenty chance that the measurement doesn’t fit what we were expecting. If it falls inside then we have what’s known as the null hypothesis, that there isn’t any noticeable effect for that particular measurement.

Deming’s point was that in most processes any effect that the individual may have is swamped by the system their are part of, in fact the variability they cause is just part of that system overall. So if measurements are falling within the confidence limits you can’t point to one person over another and say they’re better or worse.

So changing things, for better or worse, mean you have to change the entire system. It’s an iron rule, the system always wins. No amount of arbitrary targets, shouting, or wishing can change this. I cover this in more detail in the video talks on my consultancy website.

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