Chapter 8: Problem 8
Beta-Darstellung der Binomialverteilung. Zeigen Sie durch Differentiation nach \(p:\) Für alle \(0
Short Answer
Expert verified
The binomial probability sum equals the Beta function integral over [0, p].
Step by step solution
01
Understand the Problem
We need to show that the sum of probabilities from \(k+1\) to \(n\), denoted as \(\mathscr{B}_{n,p}(\{k+1, k+2, \ldots, n\})\), can be expressed as a certain integral involving Beta functions. This includes demonstrating the equivalency between the given binomial probability configuration and a Beta probability integral over the interval \([0, p]\).
02
Recall Binomial Probability Sum
For a binomial distribution, the probability of getting at least \(k+1\) successes out of \(n\) trials is given by the cumulative binomial distribution function from \(k+1\) to \(n\). This is expressed as a sum of terms, \[ \mathscr{B}_{n,p}(\{k+1, k+2, \ldots, n\}) = \sum_{j=k+1}^{n} \binom{n}{j} p^j (1-p)^{n-j} \].
03
Set Up the Integral Representation
Recognize that the integral \( \int_{0}^{p} t^{k}(1-t)^{n-k-1} dt \) represents the cumulative distribution function of the Beta distribution. The Beta distribution function \( \beta_{k+1, n-k}([0,p]) \) is evaluated over the interval \([0, p]\), which matches the format of our problem.
04
Differentiation by Parts
To solve the given problem using differentiation, we apply the integral of Beta function, \[ B(x; a, b) = \int_{0}^{x} t^{a-1}(1-t)^{b-1} dt \]. We differentiate this with respect to \(p\) to express it in terms of \(n\), \(k\), and \(p\). After applying the Fundamental Theorem of Calculus, we find:\[ \frac{d}{dp} B(p; k+1, n-k) = p^{k}(1-p)^{n-k-1} \].
05
Understand the Resulting Expression
Integrate the differentiated expression to account for the interval \([0, p]\), thus relating it to \(\beta_{k+1, n-k}([0, p])\), and express it as the coefficient involved, which matches the binomial coefficient representation. This reflects a connection formed by completing the integral evaluation for Beta function and binomial identities.
06
Synthesis of Formulaic Equivalence
Combine the integral representation with the binomial coefficients:\[ \left( \begin{array}{c} n \ k \end{array} \right)(n-k) = \beta_{k+1, n-k}([0, p]) \].Thus, the mathematical expression translates the summation of binomial terms over \(p\) into a Beta distribution function over the same interval.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Binomial Distribution
The binomial distribution is a discrete probability distribution that models the number of successes in a sequence of independent trials. Each trial results in either success or failure. The probability of success in each trial is denoted by \( p \), while the number of trials is \( n \). The probability of getting exactly \( k \) successes in \( n \) trials is given by the formula:
- \( P(X = k) = \binom{n}{k} p^k (1-p)^{n-k} \)
- Here, \( \binom{n}{k} \) is the binomial coefficient, which counts the number of ways to choose \( k \) successes out of \( n \) trials.
- The term \( p^k (1-p)^{n-k} \) represents the probability of exactly \( k \) successes and \( n-k \) failures.
Beta Function
The Beta function is a special function in mathematics that appears in numerous probability and calculus applications. It is defined as an integral for positive \( x \) and \( y \):
- \( B(x, y) = \int_0^1 t^{x-1} (1-t)^{y-1} dt \)
- This integral involves the product of power functions \( t^{x-1} \) and \( (1-t)^{y-1} \).
Integral Representation
An integral representation refers to expressing a mathematical object, such as a function or distribution, using an integral. In the context of probability theory, this is often used to transition from discrete to continuous formulations.
- The exercise involves representing a sum of binomial probabilities as an integral over a continuous range \([0, p]\).
- The integral \( \int_0^p t^k (1-t)^{n-k-1} dt \) provides the continuous form.
Differentiation
Differentiation is a fundamental mathematical tool used to find the rate at which a function changes. It is crucial in both calculus and probability theory for analyzing changes and solving equations.
- In the given exercise, differentiation is used to transition from the Beta function integral to variable terms, particularly \( p \).
- This is achieved by differentiating the integral \( B(p; k+1, n-k) \) with respect to \( p \).
Cumulative Distribution Function
A cumulative distribution function (CDF) provides the probability that a random variable is less than or equal to a certain value. It adds up probabilities from a probability distribution.
- The CDF of a binomial distribution provides the probability of obtaining \( k \) or fewer successes in \( n \) trials.
- Mathematically, a CDF is represented as: \[ F(x) = P(X \leq x) \]
- For the Beta function, its cumulative form is expressed through an integral that evaluates this probability over a range \([0, p]\).