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/

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23 views

Equation for weighted mean of percentages

I am trying to get the equation for a weighted average of percentages to be normalized between 0 and 1. Am I doing it correctly? Thank you so much!
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How do you convert a Pisa Score to an average National IQ?

I was wondering if it is possible to convert a nation's Pisa score to its national IQ score? If it is how would you go about it? What is the formula?
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67 views

Coefficient of variation for log (base 10) transformed data set

I've recently become aware that there are different formulas for calculating the coefficient of variation (CV). It is my understanding that for numeric data this formula is used CV=(SDTEV/MEAN)100 as ...
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17 views

How to scale data proportionality as to equal 100%

I am applying for a grant for the nonprofit I run, and I have some data they need for the grant. However, this data does not equal to 100% and I need to know how to scale the data up so that it is ...
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1answer
125 views

Modelling exchange rates: how to log transform percentage changes?

I'm trying to model an exchange rate to test for extreme values. However, I have percentage changes from day to day. Given some changes are negative, I can't take the logarithm. Any idea how I could ...
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1answer
177 views

How to calculate 'times likely' for a percentage and whole number data set?

I'm analyzing speech data for single people vs those in group. I have two types of datasets for which I want to calculate "times likely". ...
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1answer
33 views

Finding the number of teams

I played in a online tournament of a game of some sorts, and I want to know how many teams they were. I have the following informations : The team who finished in first place were on the Top 0.001% ...
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1answer
73 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\...
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1answer
69 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)={\...
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121 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 ...
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1answer
37 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 ...
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1answer
23 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 ...
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173 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 ...
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1answer
52 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 ...
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47 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: ...
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1answer
54 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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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 ...
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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
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1answer
160 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.
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1answer
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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 ...
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1answer
48 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 ...
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1answer
29 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 : ...
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1answer
30 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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1answer
54 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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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}...
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1answer
373 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 [\...
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1answer
4k 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 ...
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1answer
263 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 ...
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1answer
867 views

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

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 general summary statistics) is the number of ...
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0answers
95 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,\...
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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 ...
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1answer
636 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 ...
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47 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 ...
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2answers
268 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
95 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 ...
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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 ...
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1answer
69 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 ...
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2answers
5k 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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720 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\...
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51 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 ...
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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 ...
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1answer
40 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?
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1answer
12k 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 ...
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1answer
13k 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 "?".
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2answers
43 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 ...
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2answers
203 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'...
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1answer
524 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 ...
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1answer
39 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
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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.
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1answer
152 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 - ...