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--- title: "binomial distribution" source: https://www.jemoka.com/posts/kbhbinomial_distribution/ --- A binomial distribution is a typo of distribution whose contents are: Binary Independent Fixed number Same probability: “That means: WITH REPLACEMENT” Think: “what’s the probability of \(n\) coin flips getting \(k\) heads given the head’s probability is \(p\)”. constituents We write: \begin{equation} X \sim Bin(n,p) \end{equation} where, \(n\) is the number of trials, \(p\) is the probability of success on each trial. requirements Here is the probability mass function: \begin{equation} P(X=k) = {n \choose k} p^{k}(1-p)^{n-k} \end{equation} additional information properties of binomial distribution expected value: \(np\) variance: \(np(1-p)\) deriving the expectation The expectation of the binomial distribution is derivable from the fact: \begin{equation} X = \sum_{i=1}^{n} Y_{i} \end{equation} where, \begin{equation} \begin{cases} X \sim Bin(n,p) \\ Y_{i} \sim Bern(p) \end{cases} \end{equation} Now, recall that expected value is linear. Therefore, we can write that: approximating binomial normal distribution approximation: \(n > 20\), variance large \((np(1-p)) > 10\), absolute independence; beware of continuity correction poisson distribution approximation: \(n > 20\), p small \(p < 0.05\) adding binomial distribution For \(X\) and \(Y\) independent binomial distributions, with equivalent probability: \begin{equation} X \sim Bin(a, p), Y \sim Bin(b, p) \end{equation} Then: \begin{equation} X+Y \sim Bin(a+b, p) \end{equation}