“Verbal Probability Expressions In National Intelligence Estimates: A Comprehensive Analysis Of Trends From The Fifties Through Post-9/11”, 2008-05 (; backlinks; similar):
This research presents the findings of a study that analyzed words of estimators probability in the key judgments of National Intelligence Estimates from the 1950s through the 2000s. The research found that of the 50 words examined, only 13 were statistically-significant. Furthermore, interesting trends have emerged when the words are broken down into English modals, terminology that conveys analytical assessments and words employed by the National Intelligence Council as of 2006. One of the more intriguing findings is that use of the word will has by far been the most popular for analysts, registering over 700 occurrences throughout the decades; however, a word of such certainty is problematic in the sense that intelligence should never deal with 100% certitude. The relatively low occurrence and wide variety of word usage across the decades demonstrates a real lack of consistency in the way analysts have been conveying assessments over the past 58 years. Finally, the researcher suggests the Kesselman List of Estimative Words for use in the IC. The word list takes into account the literature review findings as well as the results of this study in equating odds with verbal probabilities.
[Rachel’s lit review, for example, makes for very interesting reading. She has done a thorough search of not only the intelligence but also the business, linguistics and other literatures in order to find out how other disciplines have dealt with the problem of “What do we mean when we say something is ‘likely’…” She uncovered, for example, that, in medicine, words of estimative probability such as “likely”, “remote” and “probably” have taken on more or less fixed meanings due primarily to outside intervention or, as she put it, “legal ramifications”. Her comparative analysis of the results and approaches taken by these other disciplines is required reading for anyone in the Intelligence Community trying to understand how verbal expressions of probability are actually interpreted. The NICs list only became final in the last several years so it is arguable whether this list of nine words really captures the breadth of estimative word usage across the decades. Rather, it would be arguable if this chart didn’t make it crystal clear that the Intelligence Community has really relied on just two words, “probably” and “likely” to express its estimates of probabilities for the last 60 years. All other words are used rarely or not at all.
Based on her research of what works and what doesn’t and which words seem to have the most consistent meanings to users, Rachel even offers her own list of estimative words along with their associated probabilities:
Almost certain: 86–99%
Highly likely: 71–85%
Likely: 56–70%
Chances a little better [or less] than even: 46–55%
Unlikely: 31–45%
Highly unlikely: 16–30%
Remote: 1–15%
]
[cf. “Decision by sampling”, et al 2006; “Processing Linguistic Probabilities: General Principles and Empirical Evidence”, 1995.]