It’s as if the
blobs are accentuating the hard “reality-ness” of the thing they are
representing. They are saying: “See this line with blobs on it? The
blobs are showing something concrete, something tangible, something real. Something so real that
you can practically touch it.” Whereas the blob-free lines, they are
just abstract theoretical constructs based on formulae.
another thing. SPC’s formatting conventions even stretch to making
the blobs on the lines really quite large. Most data analysts would
flinch from making their blobs (they would probably prefer to call
them “markers” rather than “blobs”) of a size that uses so much ink. But take a look at
an SPC textbook and you’ll see large blobs.
I think this “blob factor” is a
substantial part of the appeal of SPC. Managers
see the blobs and realise instinctively that they represent concrete, measurable
things. Things that they recognise from real life. And this
immediately makes the graphs more understandable, more explainable,
If you’ve ever
Myers-Briggsed you’ll know
that one of the end results of the Myers-Briggs process is that you are assigned four letters that
basically sum you up.
The second of
these four letters will be either an N or an S. If your second
Myers-Briggs letter is an N, then you prefer to take information
in intuitively. (Yes, that’s right, the N stands for
“intuition”, which is a spectacularly unintuitive thing for
Myers-Briggs to do, but that’s a whole different story for another
day.) N preference people are more comfortable with abstract theoretical
concepts. They are more attracted to the dotted lines based on
formulae than they are to the blobs that represent the actual
If, on the
other hand, you have an S
preference, this means that you like to take information in
through your senses. The S stands for “sensing”. You literally “make
sense” of the world by seeing, hearing, touching, smelling and
tasting things. Whenever you have to disentangle a complicated
theory or concept, you probably prefer to disentangle it by working
through some practical, real life examples. Ss prefer blobs.
are mainly S preference folk. The formatting conventions of SPC
emphasise the blobs. It’s a match made in heaven.
Keeping to the straight and narrow
reason for SPC’s appeal. The ‘C’ in SPC stands for “control” and
managers need to be in control of things. Now control charts—with
their upper and lower control limits—obviously engender a sense of
control quite explicitly. But I think they also do it in a more
subtle way that affects all of us. By way of explanation, I noticed
some time ago that new Citroen C5 cars now come equipped with
a "lane departure warning system" that lets you know if you start to
wander out of your lane when you’re driving along the motorway.
According to the Citroen website, the system “detects any
unintentional lane changes at speeds of 50mph and over and vibrates
the driver’s seat on the side of the drift, prompting them to get
back on course.”
this safety feature in a glossy brochure whilst waiting for
my car to be fixed, my mind naturally enough turned to control
charts. Control charts, when you think about them, they do sort of
resemble motorway lanes, with their parallel horizontal dashed lines
exhorting you to stick to the space between them, subliminally
admonishing those who dare to transgress them. I wondered whether
we all have some kind of innate, unfulfilled desire to keep to the straight and narrow.
Is this “lane departure warning system” also part of the appeal of
Reinforcing the illusion of numeracy
When I did
A-level Economics at school, one of the teachers we had—let’s call
him Mr Burns—seemed to know pretty much nothing at all about the subject.
But he was the Head of the Economics department so the problem
wasn’t really addressed, and what actually happened was that the
other two Economics teachers just tacitly accepted the fact of their
boss's incompetence by making sure they left enough time to teach us his
bits of the syllabus as well as their own.
thing I’ll always remember about Mr Burns. In the first class he
taught us, he drew a graph of a monopoly on the blackboard. This
graph might be familiar to those of you who’ve studied Economics, and it
looks something like this:
This graph had
an almost iconic significance for Mr Burns. Here is what I think his
This is a
self-evidently complex graph. So you must be self-evidently
intelligent in order to be able to draw it on a blackboard.
Therefore you must be in command of your subject. Even though you’re
actually not, but it’s important that you need to be able to
project that kind of image because, let’s face it, you’re
the Head of Economics and people will expect you to be able to draw
and understand graphs like this. So if you can just remember how to
draw this one graph, that ought to be enough to maintain the
illusion of competence.
worry that control charts are a bit like that for some NHS managers.
A bit. Only a bit. Control charts do kind of look like the monopoly graph: lots
of lines, some of them solid, some of them dotted. Numbers. Labels.
Axes. If you draw a control chart on an office whiteboard and say
something like: “We
need to start looking at our KPIs using charts like these!” then
people will assume you’re tremendously numerate even though you’re
perhaps—how can I put this?—perhaps not quite so tremendously numerate.
The Kandy-Kolored Tangerine-Flake Streamline Baby
years ago Tom Wolfe introduced the idea of what he called “totem
A totem newspaper is the kind people don't really buy
to read but just to have, physically, because they know it supports
their own outlook on life. They're just like the buffalo tongues the
Omaha Indians used to carry around or the dog ears the Mahili clan
carried around in Bengal.
So here’s a controversial, Tom Wolfe-inspired, and somewhat zany conclusion for you.
How about we think of
control charts as
Managers don’t ask for them to study
them but just to have them, physically. They support their own
outlook on life. They reinforce an image that they are highly
numerate. They demonstrate that they are in “control” of their
department and that their indicators are sticking to the “straight
and narrow”. Oh yes, and the charts have blobs on them, which makes
at least that
part of the graph easy to explain to others.
What's not to like about all of that? No wonder SPC has sex appeal.