If all the people in the world lay on the ground, head to foot around the world, two thirds would drown.

I was a medical student when I heard this absurd statement. Perhaps I was not quite ready to see the relevance to statistical proclamations about humans, but something about it has always tickled me. Human beings are just not standard enough for statistical statements about them to remain static decade after decade. People are getting taller, larger, living longer, surviving childbirth more often, and all the while the planet remains two thirds covered by water. So what does a statistic that stays the same mean?

A good example is Herbert Spiegel’s hypnotisability scale. I never much liked the notion, but if you do it, you find 25% of the population are not hypnotisable. Stories of Erickson’s students turning up at these demonstrations and helping these non hypnotisable people experience trance in their own way, of course appeal to my mischievous side. The finding is a result of the construct of the test itself.

So what of the effectiveness of psychotherapy that has remained the same for the more than 50 years that we have been measuring it? What if it doesn’t actually say anything about people, it just measures the construct of psychotherapy and the goals therein?

Heinz Von Foerser, one of my heroes seemed to understand this kind of thing. He said that tests test the test, not the person being tested.