Emprical Probability Vs Priori Probability

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Can someone explain the difference? The Schweser notes do a pretty bad job at it….
Thanks,
Varang
 
Empirical prob are what you compute from historical data
A priori prob is your belief about the future.
In the past 5 years, let’s say that 5% of the companies listed on US stock markets went bankrupt. Using 5% to forecast the probability that a company goes bankrupt in the next year consists of using empirical probabilities.
If, on the other hand, I believe that the economy will slow down and that we will experience more bankruptcy than in the recent past, then I may assess a 10% probability that a company goes bankrupt next year. this would be an a priori probability.
 
This seems like some serious misinformation in my opinion in the above example. A BELIEF about something is a SUBJECTIVE probability, you didn’t use logic or reasoning to deduce the idea. Lemme quote the CFAI text: “a subjective probability [is] one drawing on personal or subjective judgment” page 320 of book 1
A priori probabilities are probabilities that have been deduced using logical analysis. Lemme quote the CFAI text again: “…. an a priori probability [is] one based on logical analysis rather than on observation or personal judgment” (ie. counting methods are an example). A priori probabilities are NOT subjective ie like the cfai text says, they don’t vary from person to person, they are objective.
 
iamsmart Your are show off
Madame Bovary, I think your hot
varang better learn/nail this concept now cause it will come in handy when learning Bayes Formula
 
You’ve got a bag of ten balls, three of which are red. Pick one at random.
A priori probability: P(red) = 0.3 [calculation: 3 / 10]
Empirical probability: P(red) = 0.28 [we’ve just picked 100 times and got red 28 times]
Subjective probability: P(red) = 0.5 [we’re feeling lucky]
This is neither hot, showing off, nor anything to do with Bayes. Sorry to disappoint.
 
I’m with MadameBovary on this. A priori probabilities can be objetive, subjective, drawn from a hat, based on improper priors, etc…
 
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