Tom Breur
25 August 2013
I love
travelling by train. I have gotten used to exclusively travelling by train. In
the Netherlands, I must be one of last Mohicans because their service continues to deteriorate.
Yet in all their self-reported questionnaires, they claim passengers are happy.
I guess these respondents are the only ones (like me) willing to put up with
the lack of reliability.
Dr. W. Edwards Deming introduced the
notion of “Special and Common Cause Variation”, although they appear only
slight modifications from what Shewhart referred to
as “Special and Chance Cause variation.” They describe variation in a process,
where “common” causes are the usual variations that can be predicted from past
history. Therefore, they can (easily) be quantified as expected variations from
the norm. “Special” causes cannot be quantified, simply because they haven’t
been observed before.
On Wikipedia
there is a nice overview of this topic, pointing out that “chance
variation” is like statistically ‘reliable’ noise surrounding a signal.
What has this got to do with public transportation?
When I plan to
be somewhere on time, I feel obliged
to factor in train delays. They have grown so common that it makes me look
rather silly to excuse myself being late “because the train had a delay” – well
what had you thought?!?
When there are
train connections, and I cannot afford to be late, I need to plan to arrive at
least one hour prior to my meeting, simply to avoid predictable chance cause
variation. When delays happen quite often, how “Special” can it be, then?
I remember the
first time, the train couldn’t run because autumn had dropped too many leafs on
the railroad tracks. It sounded like a joke. Now trains get cancelled for cold
weather, warm weather, and what you have.
For the
occasional train traveller, “train delay” might still be an excuse. After all:
once is an incident, twice is remarkable, and three times starts a pattern. So
unless you use the train more often, you may not have come to expect delays. For those of us who do, we
know missed connections bear no resemblance whatsoever to Black Swans…
No comments:
Post a Comment