Asked by Clarisha Nijman
on 31 Jan 2019

Dear all,

What code can I use in matlab to find the parameters of a binomial distribution? This question is very big. So I am restricting it to a specific situation.

X is binomiallly distributed with parameter n and fraction p. The parameter p is unknown.

What function in matlab can help me to find that parameter if for example it is known that X=randi(10,20,1); P(X<=4)=0.3?

Thank you in advance.

Answer by Star Strider
on 31 Jan 2019

Accepted Answer

Star Strider
on 1 Feb 2019

For that problem, this appears to be the correct approach:

X=randi(10,20,1);

Px4 = nnz(X <= 4)/numel(X); % Single Probability

[P,Pci] = binofit(Px4, numel(X)) % Binomial Probability Of A ‘Px4’ Fraction Of ‘X’ Being <= 4, Those Being Defined As A ‘Success’

If you run this several times, you will get different results for each iteration, depending on the elements of ‘X’. and therefore the value of ‘Px4’.

Clarisha Nijman
on 2 Feb 2019

That is it!!!!!!

the problem was the interpretation of the first parameter of the binofit function.

But now I understand, x is not the number of the succeses, but the probability of success in a given binomial trial based on the ACTUAL number of successes,

Once more thanks a lot!!!!

Star Strider
on 2 Feb 2019

As always, my pleasure!

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