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Questions tagged [arithmetic]

For on-topic questions involving arithmetic. Try to include also a more statistical tag. For purely mathematical questions about arithmetic, please use math SE https://math.stackexchange.com/

3
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1answer
48 views

Calculating variance of poisson distributed random variable

I am calculating variance of a Poisson distributed random variable with mean $\lambda$. I am doing it in the following way: $\mathbb{V}(X) = \mathbb{E}(X^2) - \lambda^2 \\ = \sum_{x\geq 0} \quad x^2\...
1
vote
1answer
32 views

Beta distribution, finding $\alpha, \beta$

Here the expected value and the variance are given, and it's needed to find the values of $\alpha,\beta$. From the Beta distribution and the elicited prior information, we can write: $E(\theta)={\...
0
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0answers
58 views

Negative variance of linear combination of regression coefficients

I'm going crazy over this so I hope someone can help me.. First a presentation of my case: I have a complex multiple regression model with 4 predictors (some terms that don't concern this issue are ...
0
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1answer
33 views

Simple Z-Score question dealing with normal mean and standard deviation I keep getting incorrect

The question below is simple, however, I got the question wrong despite following a basic formula I have been using for a while now. Here's the question: For applicants who actually entered medical ...
0
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1answer
19 views

Significance of Difference in arithmetic means

We characterized two social group through utilizing a 4 point likert scale and arithmetic means for 32 questions separated in 4 groups and 4 subgroups as our professor advised, we look at the ...
0
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0answers
64 views

Output Size of Mixture Density Networks

I am working on a neural network in which the final output layer will be a Mixture Density Network (MDN), but am confused about the shape of the values that final layer should return. In the paper in ...
1
vote
1answer
45 views

Squaring floats between -1 and 1 reduces sum of squares, so why do it? [duplicate]

I have been learning basic statistical testing as it relates to agriculture and have become familiar with the common practice of summing squared raw deviation values, whether in something simple like ...
0
votes
1answer
41 views

Question on finding the variance

]1 For part B, I previously had 2.07 which is incorrect but why?! I literally followed the formula and I encountered a similar problem on the internet that did the exact same thing I did done below: ...
0
votes
1answer
46 views

simply considering square root of Variance as Standard deviation

Consider the following simple linear regression equation: $$y_i=\beta_0+\beta_1 x_i+\epsilon_i,$$ where $\epsilon_i\sim N(0,\sigma^2)$. Suppose I have confidence interval of $\sigma$ which is (....
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0answers
30 views

Isn't HM a better way of averaging k fold cross validation scores than AM?

When calculating fscore we use the harmonic mean of precision and recall since hm penalizes situations when either of the two metrics is low while the other is large unlike the arithmetic mean. So ...
0
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1answer
21 views

Person months to annual risk

if a study reports a risk of 4 cases per 1000 person months can that be converted into an annual risk per 100,000 people? if so, how? Thanks
0
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1answer
35 views

Negative Binomial Coefficients -nCk = (n+k-1)Ck

I am unable to understand that why $\binom{-n}{k} = \binom{n+k-1}{k}.$ Please help me in understanding this.
0
votes
1answer
125 views

Brain teaser: 2 men can catch 2 fish in 2 minutes, at this rate, how many men can catch 500 fish in 500 minutes? [closed]

I found this interview question off of Quora. I'm unfamiliar with rate-related questions when there are 3 dimensions (men, fish, time). My intuition is: 2 men can catch 2 fish in 2 minutes then if ...
0
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1answer
45 views

Finding 'conditional probability'

Q-) The number of injury claims per month is modelled by a random variable N with: P(N=n)= 1/(n+1)(n+2),where n>=0 Determine the probability of at least 1 claim during a particular ...
0
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1answer
24 views

In Think Bayes book about Posterior mean

Page 24, Think Bayes by Allen B. Downey. Can you explain me how he compute mean by this code : ...
1
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1answer
26 views

Definition of nonarithmetic law

I came across the term nonarithmetic, but I don't now what that means. It is a condition for a Proposition of a Paper I am reading. There it is said: Assume that the law of $\ln A_0$ is nonarithmetic....
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0answers
32 views

calculating the volume price trend indicator (VPT)

Looking at this, I am still unsure how to calculate this indicator. On days when stock price goes up, multiply volume by the percentage price increase between the today's close and the previous ...
0
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1answer
38 views

Help regarding calculating z statistic and p value

I am trying to solve a problem but couldn't see any way around it. So far, here is the progress $\mu_{pop} = 10 $ $\sigma_{pop} = \sqrt12$ $\mu_{sample} = 12$ $z = (\mu_{sample} - \mu_{pop})/(\...
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0answers
25 views

Simplification of the Normal Kernel

The kernel of the normal distribution is typically written as : $ p(\theta | \mu, \sigma^2) \propto \exp\Big(- \dfrac{(\theta-\mu)^2}{2\sigma^2} \Big)$ where the normalizing constant is: $C = \dfrac{1}...
1
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1answer
298 views

Triangle inequality with random variables

Suppose $a$ and $b$ are real numbers (positive in my case), $X$ is a real-valued random variable and $F$ is a set of functions. Are the following true? $|a-b| \le E_X|a-X|+E_X|X-b|$ $|a-b| \le E_X [\...
1
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1answer
2k views

What is the underlying math needed to answer the following questions:

Some background: I was applying for an entry level business analyst position, and I was completely lost with some of these questions. These questions were from the practice test. I'm not sure how I ...
1
vote
1answer
96 views

Converting annual to daily mortality rate

In one excel workbook I am working on right now, the annual mortality rate is given as 3.082% And the formula for calculating the daily mortality rate is 1-EXP(LN(1-[annual mortality rate]/365) Why ...
0
votes
1answer
317 views

Is it better to take a mean of means or a grand mean when relaying rate data?

I apologize if this is a silly question. I am working with a dataset that includes number of fish caught in a day, and number of hours spent fishing that day. The variable of interest (outside of ...
1
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0answers
91 views

Non-linear regression model

Consider data consisting of pairs $(y_i, x_i)$ for $i = 1,..,n$ arising from a non-linear regression model: $y_i = \alpha + \beta\sin(\omega x_i + \delta) + \epsilon_i$ where $\epsilon_i \sim N(0,\...
0
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0answers
31 views

mean and least error on the line

Suppose I have a line on which i have points in non-decreasing order. My intuition tells me that if I want to minimize the squared mean error on some subset of 3 (or other number) points, I would like ...
1
vote
1answer
485 views

Geometric vs. Arithmetic mean to determine diameter of object

I want to estimate the volume of irregular objects (coral fragments) by simplifying their structure to a cylinder and then calculate the volume of this cylinder (i.e. Ecological Volume). The length ...
0
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0answers
45 views

Arithmetic and Geometric Means [duplicate]

The arithmetic and geometric averages provide a summary of historical performance. They are both unique in calculation and contain biases (as stated by my lecturer). My question is where exactly are ...
-2
votes
2answers
208 views

plotting a factorial function in R

I have problem trying to plot the following function in R: The R code I'm using is: ...
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1answer
92 views

Comparing performance of 2 comparable tests

So I have sets of data, 15 responses for test A and 15 separate responses for test B. Tests A and B have 6 perception questions and the object is to compare the performance of representing data one ...
5
votes
4answers
4k views

Converting a Model from square feet to square meter

I have a simple regression fit for predicting house prices from square feet. The estimated intercept is -44850 and the estimated slope is 280.76 To make predictions for inputs in square meters, what ...
-3
votes
1answer
67 views

How to write a fraction $\frac{n}{m}$ in the form $\frac{1}{x}$

If 663 million people don't have an item in the population of 7.3 billion, then 1 in how many people don't have it? What is the calculation I would use? How could I figure this problem for myself in ...
2
votes
2answers
3k views

Dividing or subtracting : Normal PDF's? of independent random variables [closed]

There is clear rule how to multiply OR sum Normal PDF's i.e. https://en.wikipedia.org/wiki/Sum_of_normally_distributed_random_variables $N_1(\mu_1,\sigma^2_1) + N_2(\mu_2,\sigma^2_2) = N(\mu_1+\mu_2,...
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0answers
529 views

Sufficient Statistic for inverse Gaussian Distribution

Let $X_1,...,X_n$ be a random sample from population with the pdf of the inverse Gaussian distribution $$f(x|\theta,\beta)=(\frac{\beta}{2 \pi x^3})^\frac{1}{2}e^{-\frac{\beta(x-\theta)^2}{2\...
0
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0answers
49 views

Correct term for negative difference between two values

A very newbie question! If the absolute difference between two values is the distance between them (and therefore always positive), what is the correct term for ...
3
votes
2answers
2k views

Difference between geometric and arithmetic mean

I still have problems to exactly understand the difference between geometric and arithmetic mean. I know that e.g. for returns, the arithmetic mean can be wrong (e.g. if I start with 100 $ and if my ...
1
vote
1answer
37 views

Statistic calculation (Conversion from one unit to another)

I could get the mean using the formulae but not the value of SD and IQR from using the formulae. What is the problem?
17
votes
1answer
10k views

Log probability vs product of probabilities

According to this wikipedia article, one can represent the product of probabilities x⋅y as -log(x) - log(y) making the ...
4
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1answer
9k views

What are the units of the second derivative?

Generally, what are the units of the second derivative? In this (very specific) example I have plotted height against gap probability, what should I put in place of the "?".
0
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2answers
42 views

Means in R: How to find this when the exact list is not known

This is a simple question, not really related to coding but more so to some math that I am missing in my brain. I know: An object A has a length of 5 and a mean of 4. An object B has a length of 10 ...
1
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2answers
183 views

Probability with Z-Score

Suppose that we model the distribution of IQ scores in the general population as a normal random variable with mean 100 and standard deviation 15. Find the probability that a randomly selected person'...
-1
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1answer
423 views

rescale a vector x to lie between arguments LOWER and UPPER in R [duplicate]

I am trying to rescales x to lie between lower and upper ...
-1
votes
1answer
35 views

Class Interval Ambiguity [closed]

Suppose we have to take a class interval of 5. Starting form 45 what would be my correct classes? 45-50,51-56,57-62 or 45-49,50-54,55-59
-1
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1answer
55 views

Maximum Likelihood Estimation Identity question

Is summation of logarithm of a random variable equal to the logarithm of the sum of the random variable.
4
votes
1answer
144 views

Reasons not to use fuzzy numbers instead of pds to represent uncertainty

Can someone explain why (if at all) it would be a bad idea to use fuzzy numbers in order to represent uncertainties in model parameters instead of probability distributions? To motivate my question - ...
1
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0answers
321 views

Arithmetic mean and Gini index in a grouped distribution

In the following table is represented the relative frequency distribution of 100 families related to the class of annual income (in thousands of dollars): ...
2
votes
1answer
4k views

Normalizing difference between two real values to [0,1] interval [duplicate]

If I have two positive real numbers that can take on any value between 0 and some finite real number, how do I normalized the difference between these two numbers to [0,1] interval where 0 indicates ...
1
vote
2answers
550 views

How many failed both classes

I think this might be too easy compared to other questions on this site but I really can't find the solution. ...
2
votes
0answers
59 views

Calculate $E(X)$ and $\sigma(X)$ for a simple urn problem

In a box there are 4 red and 7 green balls. A random sample of 5 of the balls is made. Let the number of red balls in the sample be $X$ (a random variable). Calculate $E(X)$ and $\sigma(X)$
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vote
2answers
7k views

How to express the difference between two percentages?

If I have some share of a product in some sector as: 2012 2013 50% 60% and I find share change for 2012-13 then should it be 10% or 0.1?
0
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0answers
92 views

How to scale a variable to a specific mean and standard deviation [duplicate]

This may be a dumb question, and I'm certain I should know this, but let's say I have one variable that has a known metric (e.g., variable A has a mean of .7 and standard deviation of .3). How do I ...