I wrote about probability before.
https://fearfunandfiloz.blogspot.com/2010/07/probability-and-money.html
I hear people asking for a judgment or opinion by saying,"On a scale from 1 to 10…" We moderns are used to using a scale from 0 to 100. We even have a symbol on our keyboards, the "per cent" sign, %, to mean we are using such a scale. "Per Cent" or "by the hundreds."
I have read that humans have some ability to estimate ratio or proportion naturally. They can make sense of the question "Is that dog twice as heavy as the other one" From gambling and games, emerged the impetus to think mathematically about probability. From probability, statistics, operations research and many sciences, including meteorology, people have developed and become accustomed to using probability statements about events that haven't happened yet.
In an attempt to be clear and definite about meanings and procedures, "frequentist" ideas of probability were used for a long time. So, a probability of a success = number of successes/ number of successes + number of failures. But to use that definition, we needed actual numbers. How many successes have there been? How many failures?
For many events, there are no precedents. What are Irene's chances in the beauty contest? She has not been in any contests before. Mrs. X thinks she has little chance while Mrs. Y "likes" her chances. So, we ask the ladies to give us a number, a percentage if they aren't scared by the word, that represents how likely they think Irene will win. Mrs. X gives her a 10% chance while Mrs. Y says 70%.
For a while, frequentists sneered at such numbers and especially at calculations done with them. There are still plenty of people who have little faith in predictions or numerical expressions of chances. However, gamblers, insurers, beauty contests officials and fans, and some psychologists pay attention. For instance, in doing my doctoral work, I read that events that have a 70% chance, in say, a game, "feel" like a certainty to many people.
Modern weather forecasting makes regular use of subjective probabilities and citizens come to expect them. The Nate Silver numbers-based organization and website "538" recently reported they had tested themselves and were happy to have found that events they tended to give a 70% chance seemed to have happened about 70% of the time.
