This article is from the source 'guardian' and was first published or seen on . It last changed over 40 days ago and won't be checked again for changes.

You can find the current article at its original source at http://www.theguardian.com/news/datablog/2015/aug/14/how-probable-is-probable

The article has changed 2 times. There is an RSS feed of changes available.

Version 0 Version 1
How probable is "probable"? How probable is 'probable'?
(34 minutes later)
This is a chart showing an experiment with 23 Nato officers asking what they understood by different terms expressing probability such as “almost certainly”, “we doubt” and “almost no chance”.This is a chart showing an experiment with 23 Nato officers asking what they understood by different terms expressing probability such as “almost certainly”, “we doubt” and “almost no chance”.
The visualisation, which surfaced on Reddit this week, was inspired by the work of pioneering intelligence analyst Sherman Kent.The visualisation, which surfaced on Reddit this week, was inspired by the work of pioneering intelligence analyst Sherman Kent.
The officers were asked to assign a percentage of probability to what they understood by the different phrases. The dots on the chart are their answers, while the grey shaded areas are roughly the ranges that Kent said should cover the probability of each description.The officers were asked to assign a percentage of probability to what they understood by the different phrases. The dots on the chart are their answers, while the grey shaded areas are roughly the ranges that Kent said should cover the probability of each description.
As you can see there is considerable discrepancy between how the different officers answered. This was a key issue to Kent’s work. In a seminal 1964 piece outlining the issue, he talked of an “early brush with ambiguity”.As you can see there is considerable discrepancy between how the different officers answered. This was a key issue to Kent’s work. In a seminal 1964 piece outlining the issue, he talked of an “early brush with ambiguity”.
The analysis started with a report about the probability of an invasion of Yugoslavia in 1951. It concluded: “Although it is impossible to determine which course the Kremlin is likely to adopt, we believe that the extent of satellite military and propaganda preparations indicates that an attack on Yugoslavia in 1951 should be considered a serious possibility.”The analysis started with a report about the probability of an invasion of Yugoslavia in 1951. It concluded: “Although it is impossible to determine which course the Kremlin is likely to adopt, we believe that the extent of satellite military and propaganda preparations indicates that an attack on Yugoslavia in 1951 should be considered a serious possibility.”
A few days after the estimate appeared, I was in informal conversation with the policy planning staff’s chairman. We spoke of Yugoslavia and the estimate. Suddenly he said: “By the way, what did you people mean by the expression ‘serious possibility’? What kind of odds did you have in mind?” I told him that my personal estimate was on the dark side, namely, that the odds were around 65 to 35 in favour of an attack. He was somewhat jolted by this; he and his colleagues had read “serious possibility” to mean odds very considerably lower.A few days after the estimate appeared, I was in informal conversation with the policy planning staff’s chairman. We spoke of Yugoslavia and the estimate. Suddenly he said: “By the way, what did you people mean by the expression ‘serious possibility’? What kind of odds did you have in mind?” I told him that my personal estimate was on the dark side, namely, that the odds were around 65 to 35 in favour of an attack. He was somewhat jolted by this; he and his colleagues had read “serious possibility” to mean odds very considerably lower.
In a military intelligence environment these semantic misunderstandings based on wording could have a serious impact; namely, action being taken or not based on overestimations or underestimations of the content of intelligence reports.In a military intelligence environment these semantic misunderstandings based on wording could have a serious impact; namely, action being taken or not based on overestimations or underestimations of the content of intelligence reports.
To deal with this, Kent and a colleague created different gradations of probability. To each they assigned a percentage range:To deal with this, Kent and a colleague created different gradations of probability. To each they assigned a percentage range:
Certainty: 100%Almost certain: 93% (give or take about 6%)Probable: 75% (give or take about 12%)Chances about even: 50%Probably not: 30% (give or take about 10%)Almost certainly not: 7% (give or take about 5%)Certainty: 100%Almost certain: 93% (give or take about 6%)Probable: 75% (give or take about 12%)Chances about even: 50%Probably not: 30% (give or take about 10%)Almost certainly not: 7% (give or take about 5%)
But the analyst faced resistance from colleagues. Although Kent described these critics as “poets” rather than mathematicians, his initiative was not backed by the national intelligence community.But the analyst faced resistance from colleagues. Although Kent described these critics as “poets” rather than mathematicians, his initiative was not backed by the national intelligence community.
Even the well-disciplined intelligence brotherhood similarly quails before the difficult but not impossible estimate and all too often resorts to an expression of avoidance drawn from a more elegant lexicon. What we consciously or subconsciously seek is an expression which conveys a definite meaning but at the same time either absolves us completely of the responsibility or makes the estimate at enough removes from ourselves as not to implicate us. The “serious [or distinct] possibility” clan of expressions is a case in point.Even the well-disciplined intelligence brotherhood similarly quails before the difficult but not impossible estimate and all too often resorts to an expression of avoidance drawn from a more elegant lexicon. What we consciously or subconsciously seek is an expression which conveys a definite meaning but at the same time either absolves us completely of the responsibility or makes the estimate at enough removes from ourselves as not to implicate us. The “serious [or distinct] possibility” clan of expressions is a case in point.
Since then there have been a number of other attempts to refine the concept of “Words of estimative probability”.Since then there have been a number of other attempts to refine the concept of “Words of estimative probability”.