You (female) discover the woman underwear that is not yours in your closet when you return from a business trip.

You wonder if your partner (male) has an affair.

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Condition: You discover the underwear.

Hypothesis: Your partner has an affair.

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In order to estimate the hypothesis by basian, you need at least three parameters.

(1)First of all, you have to estimate the probability of the underwear existence under the condition of "your partner has an affair".

- In this case, the underwear is a panty.

- There seems to be no explanation of the reason that the panty exist here.

- However, your partner should act carefully if he has an affair.

You estimate that the probability of the panty existence is 50%, if your partner has an affair.

(2)Next, you have to estimate the probability of the underwear existence under the condition of "your partner doesn't have an affair".

- Your partner bought the panty instead of a handkerchief by mistake.

- It is a panty of your friend. She just left it.

- Your partner tries to give you the panty as a present.

- (You would not want to think, but) it is his panty.

You estimate that the probability of the panty existence is 5%, if your partner doesn't has an affair.

(3)Finally, you have to estimate the (prior) probability of "your partner has an affair".

There is data that 4% of married partner betray spouse, so you adopt this.

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Question.

Calculate the probability of your partner's affair when you find a panty that is not yours.

("The signal and the noise" P.266-268 Nate Silver)

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I think it is very interesting if the problem will be the college examination.

I am sure that statistics and mathematics become familiar with high school students absolutely.

Previously, I tried to calculate the same pattern's problem (Disease incidence and medication) by Basian , and finally I needed more than three hours and ten calculation sheets.

I had enough of such calculation, now I use a tool "BAYONET" that is presented by NTT DATA Mathematical Systems Co.Ltd.

As the result, I could get the answer of "29%" as the same of the book that told me.

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Even if a panty is in your chest, the possibility of your partner's affair is still around 29 percent.

It is not enough to cross-examine your partner. 。

You should look for further evidence, and increase the confidence by the recalculation.