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A routine exercise designed to test one's knowledge; often from a textbook, course, or test used for a class or self-study. This community's policy is to "provide helpful hints" for such questions rather than complete answers.
31
votes
4
answers
2k
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Is the result of an exam a binomial?
Is X binomial distributed?
The professor's answer was:
Yes, because there is only right or wrong answers.
My answer:
No, because each question has a different "success-probability" p. … As I did understand a binomial distribution is just a series of Bernoulli-experiments, which each have a simple outcome (success or failure) with a given success-probability p (and all are "identical" …
27
votes
Accepted
Will the fact that my Italian son is going to attend a primary school change the expected nu...
B is the binomial distribution. … Note that starting with $E(X|X\geq1)$ does not give the proper answer, as knowing that a specific child is Italian violates the exchangeability assumed by the binomial distribution. …
26
votes
Accepted
Is the result of an exam a binomial?
Your professors answer assumes that all questions have same probability of "success" and are independent, since binomial is a distribution of a sum of $n$ i.i.d. Bernoulli trials. … The distribution could be approximated with binomial, or Poisson, but that's all. Otherwise you're making the i.i.d. assumption. …
25
votes
What is the expected number of children until having the same number of girls and boys?
There are $Binomial[2n,n]/(2n-1)$ ways for the couple to achieve parity for the first time with $n$ boys and $n$ girls. These are twice the Catalan numbers. … So the expected value would be
$$\sum \frac{Binomial[2n,n]}{(2n-1)2^{2n}}2n $$ but the sum is divergent: the expected number of children is infinite. …
22
votes
Accepted
What must someone know in statistics and machine learning?
There are a few crucial distributions everyone must know: Normal, Binomial, Beta, Chi-Squared, F, Student's t, Multivariate Normal. …
22
votes
Accepted
How does the beta prior affect the posterior under a binomial likelihood
To answer your first question we just need to use Bayes' Theorem to update our binomial likelihood with the beta prior. … Now, let $x_i\sim\text{Binomial}(N_i,\theta)$ and $\theta\sim\text{Beta}(\alpha,\beta)$. …
21
votes
How to assess whether a coin tossed 900 times and comes up heads 490 times is biased?
Then the number of heads has *binomial distribution with mean $(900)(1/2)=450$, and standard deviation $\sqrt{(900)(1/2)(1/2)}=15$. … In the normal approximation to the binomial, we get a better approximation to the probability that the binomial is $\ge 490$ by calculating the probability that the normal is $\ge 489.5$. …
21
votes
Risk of extinction of Schrödinger's cats
It's unclear what "risk of extinction category" means, but it appears the question asks to compute the distribution of the sum of 15 independent binomial variates having the given expectations. …
16
votes
Accepted
Unbiased estimator of variance of binomial variable
. $$
As you see we do not need the hypothesis that the variables have a binomial distribution (except implicitly in the fact that the variance exists) in order to derive this estimator. …
15
votes
How to choose the null and alternative hypothesis?
.$$ This is a one-sided binomial proportion test. $H_a$ is the statement that, if it were true, would need to be strongly supported by the data we collected. …
14
votes
Accepted
Probability of each of the three Christmas puddings having exactly 2 coins
$Pr(A=2)$ is a simple binomial calculation: $A\sim Binom(6, 1/3)$, so $Pr(A=2) = {6\choose 2}(1/3)^2(2/3)^4 = 80/243$. …
14
votes
1
answer
13k
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Log Likelihood for GLM
library(bbmle)
#successes in first column, failures in second
Y <- matrix(c(1,2,4,3,2,0),3,2)
#predictor
X <- c(0,1,2)
#use glm
fit.glm <- glm(Y ~ X,family=binomial (link=logit))
summary(fit.glm)
# …
13
votes
Probability that fewer than 24 people logging into the site will make a purchase
However, if (oblivious to a continuity correction) you take the key probability to be $P(X < 24),$ round excessively, and
do a normal approximation to binomial using printed tables, you get $0.8264.$ …
13
votes
How to assess whether a coin tossed 900 times and comes up heads 490 times is biased?
Therefore, the number of heads thrown in 900 tries, $X$, has a ${\rm Binomial}(900,\frac{1}{2})$ distribution under the null hypothesis of a fair coin. … We know that the mass function for $ Y \sim {\rm Binomial}(n,p)$, is
$$ P(Y = y) = \binom{n}{y} p^y (1-p)^{n-y} $$
I'll leave it to you to calculate $p$-value you seek. …
12
votes
A meeting has 12 employees. Given that 8 of the employees are female, what is the probabilit...
.$$
Consequently, the number of females in the group has a binomial distribution:
$$\dot{X} \equiv \sum_{i} X_i \sim \text{Bin}(12, \tfrac{1}{2}),$$
and the conditional probability of interest is:
$$\mathbb …