![]() Likelihood of “rare” PhenomenaĮxample of life events with the same level of likelihoodĮxample of events with the same likelihood range than event xīeing born a twin, NB: actually it is around 3.3%ĭrawing an ace from a 52 cards deck (4/52=7.7%) Here again, the last two columns to the right display the “Frequency equivalent” and the corresponding probability to see the event “next year”: at the end of this text you will find an explanation related to these two columns. Going below would require solid data and it is highly recommended to stay away from that. The Table starts where the prior finished (0.1) and reaches 10 -6 as this value is commonly considered as the threshold value of human credibility. Making sense of probabilities and frequencies : step 2 NB: a non expert should stop here at this level of scrutiny.Įxperts can develop more in depth estimates for lower probabilities levels using the next table below. Mortality rate of SARS (11%) of people diagnosed with the disease. Getting stuck for more than one hour in traffic (exclude commuting).Ĭhance of drawing 1 when drawing a fair dice (1/6=0.16) That a person between the age of 18 and 29 does NOT read a newspaper regularlyĭivorcing, depending on the country (reportedly 30-40%).Ī celebrity marriage will last a lifetime. Getting stuck in a traffic jam for at least 20 minutes next year (exclude commuting).Ī member of the family gets a cold next year. If these events occur with a known average rate and independently of the time since the last event.Īt least one sunny week-end in the next year.įinding at least one container of ice cream in a family freezer. Everyday vocabulary used to describe the event x.Įxample of life events x with the same level of likelihoodĮxample of events with the same level of likelihood than event x The last two columns to the right display the “Frequency equivalent” and the corresponding probability to see the event “next year”: at the end of this text you will find an explanation related to these two columns. For low probabilities p x=<0.1 trained analysts can use the Table delivered in step 2 which zooms into the lower range of probabilities. The Table below can be used for estimating a large probability, high frequency event -x. If you want to stay out of jail never use nil or one! Making sense of probabilities and frequencies : step 1 Nil means it is impossible to occur, one means it is certain to occur. Probability is by definition a number between nil and one, measuring the chances some event may or may not happen. One can measure frequency by long term observations (building a “statistic”). For people in charge of performing risk assessments a common unit of time is “per year”. One can always replace time by other “counters”. Making sense of probabilities and frequencies : definitionsįrequency is a measure of how often an event occurs on average during a unit of time (how many times an engine supposed to start every morning fails to start per year). Furthermore, when using a consistent approach, the relative estimates of probabilities will be consistent among each other. That results in expanding the estimate range while strongly reducing the “s.t in-s.t-out” syndrome. That requires no “statistical” calculations, and by doing so the user transparently acknowledges uncertainties. In reality, making sense of probabilities and frequencies allows to simply define ranges of probabilities and frequencies based on analogies and tables. As a result users embrace index-approaches (probabilities are given (absurd) values like 1,2,3.n), qualitative approaches (small, medium, large… “fast-food style”) while believing they will get a good understanding of their risks out of this. Their justification includes that probabilities are complicated, they require “statistics”. Oftentimes users feel compelled to use qualitative approaches to risk assessments. Making sense of probabilities and frequencies (in a quantitative way) is necessary to benefit from better risk assessment. ![]() Making sense of Probabilities and Frequencies
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